From 844c971d8aeb2693bc01739963f5da675b989d03 Mon Sep 17 00:00:00 2001 From: Kirill Volinsky Date: Sat, 2 Aug 2014 14:17:32 +0000 Subject: added pcre16 project git-svn-id: http://svn.miranda-ng.org/main/trunk@10019 1316c22d-e87f-b044-9b9b-93d7a3e3ba9c --- plugins/Pcre16/docs/doc/html/pcreapi.html | 2922 +++++++++++++++++++++++++++++ 1 file changed, 2922 insertions(+) create mode 100644 plugins/Pcre16/docs/doc/html/pcreapi.html (limited to 'plugins/Pcre16/docs/doc/html/pcreapi.html') diff --git a/plugins/Pcre16/docs/doc/html/pcreapi.html b/plugins/Pcre16/docs/doc/html/pcreapi.html new file mode 100644 index 0000000000..b401ecc76d --- /dev/null +++ b/plugins/Pcre16/docs/doc/html/pcreapi.html @@ -0,0 +1,2922 @@ + + +pcreapi specification + + +

pcreapi man page

+Return to the PCRE index page. +

+This page is part of the PCRE HTML documentation. It was generated automatically +from the original man page. If there is any nonsense in it, please consult the +man page, in case the conversion went wrong. +
+

PCRE NATIVE API BASIC FUNCTIONS +
PCRE NATIVE API STRING EXTRACTION FUNCTIONS +
PCRE NATIVE API AUXILIARY FUNCTIONS +
PCRE NATIVE API INDIRECTED FUNCTIONS +
PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES +
PCRE API OVERVIEW +
NEWLINES +
MULTITHREADING +
SAVING PRECOMPILED PATTERNS FOR LATER USE +
CHECKING BUILD-TIME OPTIONS +
COMPILING A PATTERN +
COMPILATION ERROR CODES +
STUDYING A PATTERN +
LOCALE SUPPORT +
INFORMATION ABOUT A PATTERN +
REFERENCE COUNTS +
MATCHING A PATTERN: THE TRADITIONAL FUNCTION +
EXTRACTING CAPTURED SUBSTRINGS BY NUMBER +
EXTRACTING CAPTURED SUBSTRINGS BY NAME +
DUPLICATE SUBPATTERN NAMES +
FINDING ALL POSSIBLE MATCHES +
OBTAINING AN ESTIMATE OF STACK USAGE +
MATCHING A PATTERN: THE ALTERNATIVE FUNCTION +
SEE ALSO +
AUTHOR +
REVISION +

+#include <pcre.h> +

+
PCRE NATIVE API BASIC FUNCTIONS
+

+pcre *pcre_compile(const char *pattern, int options, + const char **errptr, int *erroffset, + const unsigned char *tableptr); +
+
+pcre *pcre_compile2(const char *pattern, int options, + int *errorcodeptr, + const char **errptr, int *erroffset, + const unsigned char *tableptr); +
+
+pcre_extra *pcre_study(const pcre *code, int options, + const char **errptr); +
+
+void pcre_free_study(pcre_extra *extra); +
+
+int pcre_exec(const pcre *code, const pcre_extra *extra, + const char *subject, int length, int startoffset, + int options, int *ovector, int ovecsize); +
+
+int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, + const char *subject, int length, int startoffset, + int options, int *ovector, int ovecsize, + int *workspace, int wscount); +

+
PCRE NATIVE API STRING EXTRACTION FUNCTIONS
+

+int pcre_copy_named_substring(const pcre *code, + const char *subject, int *ovector, + int stringcount, const char *stringname, + char *buffer, int buffersize); +
+
+int pcre_copy_substring(const char *subject, int *ovector, + int stringcount, int stringnumber, char *buffer, + int buffersize); +
+
+int pcre_get_named_substring(const pcre *code, + const char *subject, int *ovector, + int stringcount, const char *stringname, + const char **stringptr); +
+
+int pcre_get_stringnumber(const pcre *code, + const char *name); +
+
+int pcre_get_stringtable_entries(const pcre *code, + const char *name, char **first, char **last); +
+
+int pcre_get_substring(const char *subject, int *ovector, + int stringcount, int stringnumber, + const char **stringptr); +
+
+int pcre_get_substring_list(const char *subject, + int *ovector, int stringcount, const char ***listptr); +
+
+void pcre_free_substring(const char *stringptr); +
+
+void pcre_free_substring_list(const char **stringptr); +

+
PCRE NATIVE API AUXILIARY FUNCTIONS
+

+int pcre_jit_exec(const pcre *code, const pcre_extra *extra, + const char *subject, int length, int startoffset, + int options, int *ovector, int ovecsize, + pcre_jit_stack *jstack); +
+
+pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize); +
+
+void pcre_jit_stack_free(pcre_jit_stack *stack); +
+
+void pcre_assign_jit_stack(pcre_extra *extra, + pcre_jit_callback callback, void *data); +
+
+const unsigned char *pcre_maketables(void); +
+
+int pcre_fullinfo(const pcre *code, const pcre_extra *extra, + int what, void *where); +
+
+int pcre_refcount(pcre *code, int adjust); +
+
+int pcre_config(int what, void *where); +
+
+const char *pcre_version(void); +
+
+int pcre_pattern_to_host_byte_order(pcre *code, + pcre_extra *extra, const unsigned char *tables); +

+
PCRE NATIVE API INDIRECTED FUNCTIONS
+

+void *(*pcre_malloc)(size_t); +
+
+void (*pcre_free)(void *); +
+
+void *(*pcre_stack_malloc)(size_t); +
+
+void (*pcre_stack_free)(void *); +
+
+int (*pcre_callout)(pcre_callout_block *); +
+
+int (*pcre_stack_guard)(void); +

+
PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
+

+As well as support for 8-bit character strings, PCRE also supports 16-bit +strings (from release 8.30) and 32-bit strings (from release 8.32), by means of +two additional libraries. They can be built as well as, or instead of, the +8-bit library. To avoid too much complication, this document describes the +8-bit versions of the functions, with only occasional references to the 16-bit +and 32-bit libraries. +

+The 16-bit and 32-bit functions operate in the same way as their 8-bit +counterparts; they just use different data types for their arguments and +results, and their names start with pcre16_ or pcre32_ instead of +pcre_. For every option that has UTF8 in its name (for example, +PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8 replaced +by UTF16 or UTF32, respectively. This facility is in fact just cosmetic; the +16-bit and 32-bit option names define the same bit values. +

+References to bytes and UTF-8 in this document should be read as references to +16-bit data units and UTF-16 when using the 16-bit library, or 32-bit data +units and UTF-32 when using the 32-bit library, unless specified otherwise. +More details of the specific differences for the 16-bit and 32-bit libraries +are given in the +pcre16 +and +pcre32 +pages. +

+
PCRE API OVERVIEW
+

+PCRE has its own native API, which is described in this document. There are +also some wrapper functions (for the 8-bit library only) that correspond to the +POSIX regular expression API, but they do not give access to all the +functionality. They are described in the +pcreposix +documentation. Both of these APIs define a set of C function calls. A C++ +wrapper (again for the 8-bit library only) is also distributed with PCRE. It is +documented in the +pcrecpp +page. +

+The native API C function prototypes are defined in the header file +pcre.h, and on Unix-like systems the (8-bit) library itself is called +libpcre. It can normally be accessed by adding -lpcre to the +command for linking an application that uses PCRE. The header file defines the +macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release numbers +for the library. Applications can use these to include support for different +releases of PCRE. +

+In a Windows environment, if you want to statically link an application program +against a non-dll pcre.a file, you must define PCRE_STATIC before +including pcre.h or pcrecpp.h, because otherwise the +pcre_malloc() and pcre_free() exported functions will be declared +__declspec(dllimport), with unwanted results. +

+The functions pcre_compile(), pcre_compile2(), pcre_study(), +and pcre_exec() are used for compiling and matching regular expressions +in a Perl-compatible manner. A sample program that demonstrates the simplest +way of using them is provided in the file called pcredemo.c in the PCRE +source distribution. A listing of this program is given in the +pcredemo +documentation, and the +pcresample +documentation describes how to compile and run it. +

+Just-in-time compiler support is an optional feature of PCRE that can be built +in appropriate hardware environments. It greatly speeds up the matching +performance of many patterns. Simple programs can easily request that it be +used if available, by setting an option that is ignored when it is not +relevant. More complicated programs might need to make use of the functions +pcre_jit_stack_alloc(), pcre_jit_stack_free(), and +pcre_assign_jit_stack() in order to control the JIT code's memory usage. +

+From release 8.32 there is also a direct interface for JIT execution, which +gives improved performance. The JIT-specific functions are discussed in the +pcrejit +documentation. +

+A second matching function, pcre_dfa_exec(), which is not +Perl-compatible, is also provided. This uses a different algorithm for the +matching. The alternative algorithm finds all possible matches (at a given +point in the subject), and scans the subject just once (unless there are +lookbehind assertions). However, this algorithm does not return captured +substrings. A description of the two matching algorithms and their advantages +and disadvantages is given in the +pcrematching +documentation. +

+In addition to the main compiling and matching functions, there are convenience +functions for extracting captured substrings from a subject string that is +matched by pcre_exec(). They are: +

+  pcre_copy_substring()
+  pcre_copy_named_substring()
+  pcre_get_substring()
+  pcre_get_named_substring()
+  pcre_get_substring_list()
+  pcre_get_stringnumber()
+  pcre_get_stringtable_entries()
+

+pcre_free_substring() and pcre_free_substring_list() are also +provided, to free the memory used for extracted strings. +

+The function pcre_maketables() is used to build a set of character tables +in the current locale for passing to pcre_compile(), pcre_exec(), +or pcre_dfa_exec(). This is an optional facility that is provided for +specialist use. Most commonly, no special tables are passed, in which case +internal tables that are generated when PCRE is built are used. +

+The function pcre_fullinfo() is used to find out information about a +compiled pattern. The function pcre_version() returns a pointer to a +string containing the version of PCRE and its date of release. +

+The function pcre_refcount() maintains a reference count in a data block +containing a compiled pattern. This is provided for the benefit of +object-oriented applications. +

+The global variables pcre_malloc and pcre_free initially contain +the entry points of the standard malloc() and free() functions, +respectively. PCRE calls the memory management functions via these variables, +so a calling program can replace them if it wishes to intercept the calls. This +should be done before calling any PCRE functions. +

+The global variables pcre_stack_malloc and pcre_stack_free are also +indirections to memory management functions. These special functions are used +only when PCRE is compiled to use the heap for remembering data, instead of +recursive function calls, when running the pcre_exec() function. See the +pcrebuild +documentation for details of how to do this. It is a non-standard way of +building PCRE, for use in environments that have limited stacks. Because of the +greater use of memory management, it runs more slowly. Separate functions are +provided so that special-purpose external code can be used for this case. When +used, these functions are always called in a stack-like manner (last obtained, +first freed), and always for memory blocks of the same size. There is a +discussion about PCRE's stack usage in the +pcrestack +documentation. +

+The global variable pcre_callout initially contains NULL. It can be set +by the caller to a "callout" function, which PCRE will then call at specified +points during a matching operation. Details are given in the +pcrecallout +documentation. +

+The global variable pcre_stack_guard initially contains NULL. It can be +set by the caller to a function that is called by PCRE whenever it starts +to compile a parenthesized part of a pattern. When parentheses are nested, PCRE +uses recursive function calls, which use up the system stack. This function is +provided so that applications with restricted stacks can force a compilation +error if the stack runs out. The function should return zero if all is well, or +non-zero to force an error. +

+
NEWLINES
+

+PCRE supports five different conventions for indicating line breaks in +strings: a single CR (carriage return) character, a single LF (linefeed) +character, the two-character sequence CRLF, any of the three preceding, or any +Unicode newline sequence. The Unicode newline sequences are the three just +mentioned, plus the single characters VT (vertical tab, U+000B), FF (form feed, +U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS +(paragraph separator, U+2029). +

+Each of the first three conventions is used by at least one operating system as +its standard newline sequence. When PCRE is built, a default can be specified. +The default default is LF, which is the Unix standard. When PCRE is run, the +default can be overridden, either when a pattern is compiled, or when it is +matched. +

+At compile time, the newline convention can be specified by the options +argument of pcre_compile(), or it can be specified by special text at the +start of the pattern itself; this overrides any other settings. See the +pcrepattern +page for details of the special character sequences. +

+In the PCRE documentation the word "newline" is used to mean "the character or +pair of characters that indicate a line break". The choice of newline +convention affects the handling of the dot, circumflex, and dollar +metacharacters, the handling of #-comments in /x mode, and, when CRLF is a +recognized line ending sequence, the match position advancement for a +non-anchored pattern. There is more detail about this in the +section on pcre_exec() options +below. +

+The choice of newline convention does not affect the interpretation of +the \n or \r escape sequences, nor does it affect what \R matches, which is +controlled in a similar way, but by separate options. +

+
MULTITHREADING
+

+The PCRE functions can be used in multi-threading applications, with the +proviso that the memory management functions pointed to by pcre_malloc, +pcre_free, pcre_stack_malloc, and pcre_stack_free, and the +callout and stack-checking functions pointed to by pcre_callout and +pcre_stack_guard, are shared by all threads. +

+The compiled form of a regular expression is not altered during matching, so +the same compiled pattern can safely be used by several threads at once. +

+If the just-in-time optimization feature is being used, it needs separate +memory stack areas for each thread. See the +pcrejit +documentation for more details. +

+
SAVING PRECOMPILED PATTERNS FOR LATER USE
+

+The compiled form of a regular expression can be saved and re-used at a later +time, possibly by a different program, and even on a host other than the one on +which it was compiled. Details are given in the +pcreprecompile +documentation, which includes a description of the +pcre_pattern_to_host_byte_order() function. However, compiling a regular +expression with one version of PCRE for use with a different version is not +guaranteed to work and may cause crashes. +

+
CHECKING BUILD-TIME OPTIONS
+

+int pcre_config(int what, void *where); +

+The function pcre_config() makes it possible for a PCRE client to +discover which optional features have been compiled into the PCRE library. The +pcrebuild +documentation has more details about these optional features. +

+The first argument for pcre_config() is an integer, specifying which +information is required; the second argument is a pointer to a variable into +which the information is placed. The returned value is zero on success, or the +negative error code PCRE_ERROR_BADOPTION if the value in the first argument is +not recognized. The following information is available: +

+  PCRE_CONFIG_UTF8
+

+The output is an integer that is set to one if UTF-8 support is available; +otherwise it is set to zero. This value should normally be given to the 8-bit +version of this function, pcre_config(). If it is given to the 16-bit +or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION. +

+  PCRE_CONFIG_UTF16
+

+The output is an integer that is set to one if UTF-16 support is available; +otherwise it is set to zero. This value should normally be given to the 16-bit +version of this function, pcre16_config(). If it is given to the 8-bit +or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION. +

+  PCRE_CONFIG_UTF32
+

+The output is an integer that is set to one if UTF-32 support is available; +otherwise it is set to zero. This value should normally be given to the 32-bit +version of this function, pcre32_config(). If it is given to the 8-bit +or 16-bit version of this function, the result is PCRE_ERROR_BADOPTION. +

+  PCRE_CONFIG_UNICODE_PROPERTIES
+

+The output is an integer that is set to one if support for Unicode character +properties is available; otherwise it is set to zero. +

+  PCRE_CONFIG_JIT
+

+The output is an integer that is set to one if support for just-in-time +compiling is available; otherwise it is set to zero. +

+  PCRE_CONFIG_JITTARGET
+

+The output is a pointer to a zero-terminated "const char *" string. If JIT +support is available, the string contains the name of the architecture for +which the JIT compiler is configured, for example "x86 32bit (little endian + +unaligned)". If JIT support is not available, the result is NULL. +

+  PCRE_CONFIG_NEWLINE
+

+The output is an integer whose value specifies the default character sequence +that is recognized as meaning "newline". The values that are supported in +ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for +ANYCRLF, and -1 for ANY. In EBCDIC environments, CR, ANYCRLF, and ANY yield the +same values. However, the value for LF is normally 21, though some EBCDIC +environments use 37. The corresponding values for CRLF are 3349 and 3365. The +default should normally correspond to the standard sequence for your operating +system. +

+  PCRE_CONFIG_BSR
+

+The output is an integer whose value indicates what character sequences the \R +escape sequence matches by default. A value of 0 means that \R matches any +Unicode line ending sequence; a value of 1 means that \R matches only CR, LF, +or CRLF. The default can be overridden when a pattern is compiled or matched. +

+  PCRE_CONFIG_LINK_SIZE
+

+The output is an integer that contains the number of bytes used for internal +linkage in compiled regular expressions. For the 8-bit library, the value can +be 2, 3, or 4. For the 16-bit library, the value is either 2 or 4 and is still +a number of bytes. For the 32-bit library, the value is either 2 or 4 and is +still a number of bytes. The default value of 2 is sufficient for all but the +most massive patterns, since it allows the compiled pattern to be up to 64K in +size. Larger values allow larger regular expressions to be compiled, at the +expense of slower matching. +

+  PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
+

+The output is an integer that contains the threshold above which the POSIX +interface uses malloc() for output vectors. Further details are given in +the +pcreposix +documentation. +

+  PCRE_CONFIG_PARENS_LIMIT
+

+The output is a long integer that gives the maximum depth of nesting of +parentheses (of any kind) in a pattern. This limit is imposed to cap the amount +of system stack used when a pattern is compiled. It is specified when PCRE is +built; the default is 250. This limit does not take into account the stack that +may already be used by the calling application. For finer control over +compilation stack usage, you can set a pointer to an external checking function +in pcre_stack_guard. +

+  PCRE_CONFIG_MATCH_LIMIT
+

+The output is a long integer that gives the default limit for the number of +internal matching function calls in a pcre_exec() execution. Further +details are given with pcre_exec() below. +

+  PCRE_CONFIG_MATCH_LIMIT_RECURSION
+

+The output is a long integer that gives the default limit for the depth of +recursion when calling the internal matching function in a pcre_exec() +execution. Further details are given with pcre_exec() below. +

+  PCRE_CONFIG_STACKRECURSE
+

+The output is an integer that is set to one if internal recursion when running +pcre_exec() is implemented by recursive function calls that use the stack +to remember their state. This is the usual way that PCRE is compiled. The +output is zero if PCRE was compiled to use blocks of data on the heap instead +of recursive function calls. In this case, pcre_stack_malloc and +pcre_stack_free are called to manage memory blocks on the heap, thus +avoiding the use of the stack. +

+
COMPILING A PATTERN
+

+Either of the functions pcre_compile() or pcre_compile2() can be +called to compile a pattern into an internal form. The only difference between +the two interfaces is that pcre_compile2() has an additional argument, +errorcodeptr, via which a numerical error code can be returned. To avoid +too much repetition, we refer just to pcre_compile() below, but the +information applies equally to pcre_compile2(). +

+The pattern is a C string terminated by a binary zero, and is passed in the +pattern argument. A pointer to a single block of memory that is obtained +via pcre_malloc is returned. This contains the compiled code and related +data. The pcre type is defined for the returned block; this is a typedef +for a structure whose contents are not externally defined. It is up to the +caller to free the memory (via pcre_free) when it is no longer required. +

+Although the compiled code of a PCRE regex is relocatable, that is, it does not +depend on memory location, the complete pcre data block is not +fully relocatable, because it may contain a copy of the tableptr +argument, which is an address (see below). +

+The options argument contains various bit settings that affect the +compilation. It should be zero if no options are required. The available +options are described below. Some of them (in particular, those that are +compatible with Perl, but some others as well) can also be set and unset from +within the pattern (see the detailed description in the +pcrepattern +documentation). For those options that can be different in different parts of +the pattern, the contents of the options argument specifies their +settings at the start of compilation and execution. The PCRE_ANCHORED, +PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and +PCRE_NO_START_OPTIMIZE options can be set at the time of matching as well as at +compile time. +

+If errptr is NULL, pcre_compile() returns NULL immediately. +Otherwise, if compilation of a pattern fails, pcre_compile() returns +NULL, and sets the variable pointed to by errptr to point to a textual +error message. This is a static string that is part of the library. You must +not try to free it. Normally, the offset from the start of the pattern to the +data unit that was being processed when the error was discovered is placed in +the variable pointed to by erroffset, which must not be NULL (if it is, +an immediate error is given). However, for an invalid UTF-8 or UTF-16 string, +the offset is that of the first data unit of the failing character. +

+Some errors are not detected until the whole pattern has been scanned; in these +cases, the offset passed back is the length of the pattern. Note that the +offset is in data units, not characters, even in a UTF mode. It may sometimes +point into the middle of a UTF-8 or UTF-16 character. +

+If pcre_compile2() is used instead of pcre_compile(), and the +errorcodeptr argument is not NULL, a non-zero error code number is +returned via this argument in the event of an error. This is in addition to the +textual error message. Error codes and messages are listed below. +

+If the final argument, tableptr, is NULL, PCRE uses a default set of +character tables that are built when PCRE is compiled, using the default C +locale. Otherwise, tableptr must be an address that is the result of a +call to pcre_maketables(). This value is stored with the compiled +pattern, and used again by pcre_exec() and pcre_dfa_exec() when the +pattern is matched. For more discussion, see the section on locale support +below. +

+This code fragment shows a typical straightforward call to pcre_compile(): +

+  pcre *re;
+  const char *error;
+  int erroffset;
+  re = pcre_compile(
+    "^A.*Z",          /* the pattern */
+    0,                /* default options */
+    &error,           /* for error message */
+    &erroffset,       /* for error offset */
+    NULL);            /* use default character tables */
+

+The following names for option bits are defined in the pcre.h header +file: +

+  PCRE_ANCHORED
+

+If this bit is set, the pattern is forced to be "anchored", that is, it is +constrained to match only at the first matching point in the string that is +being searched (the "subject string"). This effect can also be achieved by +appropriate constructs in the pattern itself, which is the only way to do it in +Perl. +

+  PCRE_AUTO_CALLOUT
+

+If this bit is set, pcre_compile() automatically inserts callout items, +all with number 255, before each pattern item. For discussion of the callout +facility, see the +pcrecallout +documentation. +

+  PCRE_BSR_ANYCRLF
+  PCRE_BSR_UNICODE
+

+These options (which are mutually exclusive) control what the \R escape +sequence matches. The choice is either to match only CR, LF, or CRLF, or to +match any Unicode newline sequence. The default is specified when PCRE is +built. It can be overridden from within the pattern, or by setting an option +when a compiled pattern is matched. +

+  PCRE_CASELESS
+

+If this bit is set, letters in the pattern match both upper and lower case +letters. It is equivalent to Perl's /i option, and it can be changed within a +pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the +concept of case for characters whose values are less than 128, so caseless +matching is always possible. For characters with higher values, the concept of +case is supported if PCRE is compiled with Unicode property support, but not +otherwise. If you want to use caseless matching for characters 128 and above, +you must ensure that PCRE is compiled with Unicode property support as well as +with UTF-8 support. +

+  PCRE_DOLLAR_ENDONLY
+

+If this bit is set, a dollar metacharacter in the pattern matches only at the +end of the subject string. Without this option, a dollar also matches +immediately before a newline at the end of the string (but not before any other +newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set. +There is no equivalent to this option in Perl, and no way to set it within a +pattern. +

+  PCRE_DOTALL
+

+If this bit is set, a dot metacharacter in the pattern matches a character of +any value, including one that indicates a newline. However, it only ever +matches one character, even if newlines are coded as CRLF. Without this option, +a dot does not match when the current position is at a newline. This option is +equivalent to Perl's /s option, and it can be changed within a pattern by a +(?s) option setting. A negative class such as [^a] always matches newline +characters, independent of the setting of this option. +

+  PCRE_DUPNAMES
+

+If this bit is set, names used to identify capturing subpatterns need not be +unique. This can be helpful for certain types of pattern when it is known that +only one instance of the named subpattern can ever be matched. There are more +details of named subpatterns below; see also the +pcrepattern +documentation. +

+  PCRE_EXTENDED
+

+If this bit is set, most white space characters in the pattern are totally +ignored except when escaped or inside a character class. However, white space +is not allowed within sequences such as (?> that introduce various +parenthesized subpatterns, nor within a numerical quantifier such as {1,3}. +However, ignorable white space is permitted between an item and a following +quantifier and between a quantifier and a following + that indicates +possessiveness. +

+White space did not used to include the VT character (code 11), because Perl +did not treat this character as white space. However, Perl changed at release +5.18, so PCRE followed at release 8.34, and VT is now treated as white space. +

+PCRE_EXTENDED also causes characters between an unescaped # outside a character +class and the next newline, inclusive, to be ignored. PCRE_EXTENDED is +equivalent to Perl's /x option, and it can be changed within a pattern by a +(?x) option setting. +

+Which characters are interpreted as newlines is controlled by the options +passed to pcre_compile() or by a special sequence at the start of the +pattern, as described in the section entitled +"Newline conventions" +in the pcrepattern documentation. Note that the end of this type of +comment is a literal newline sequence in the pattern; escape sequences that +happen to represent a newline do not count. +

+This option makes it possible to include comments inside complicated patterns. +Note, however, that this applies only to data characters. White space characters +may never appear within special character sequences in a pattern, for example +within the sequence (?( that introduces a conditional subpattern. +

+  PCRE_EXTRA
+

+This option was invented in order to turn on additional functionality of PCRE +that is incompatible with Perl, but it is currently of very little use. When +set, any backslash in a pattern that is followed by a letter that has no +special meaning causes an error, thus reserving these combinations for future +expansion. By default, as in Perl, a backslash followed by a letter with no +special meaning is treated as a literal. (Perl can, however, be persuaded to +give an error for this, by running it with the -w option.) There are at present +no other features controlled by this option. It can also be set by a (?X) +option setting within a pattern. +

+  PCRE_FIRSTLINE
+

+If this option is set, an unanchored pattern is required to match before or at +the first newline in the subject string, though the matched text may continue +over the newline. +

+  PCRE_JAVASCRIPT_COMPAT
+

+If this option is set, PCRE's behaviour is changed in some ways so that it is +compatible with JavaScript rather than Perl. The changes are as follows: +

+(1) A lone closing square bracket in a pattern causes a compile-time error, +because this is illegal in JavaScript (by default it is treated as a data +character). Thus, the pattern AB]CD becomes illegal when this option is set. +

+(2) At run time, a back reference to an unset subpattern group matches an empty +string (by default this causes the current matching alternative to fail). A +pattern such as (\1)(a) succeeds when this option is set (assuming it can find +an "a" in the subject), whereas it fails by default, for Perl compatibility. +

+(3) \U matches an upper case "U" character; by default \U causes a compile +time error (Perl uses \U to upper case subsequent characters). +

+(4) \u matches a lower case "u" character unless it is followed by four +hexadecimal digits, in which case the hexadecimal number defines the code point +to match. By default, \u causes a compile time error (Perl uses it to upper +case the following character). +

+(5) \x matches a lower case "x" character unless it is followed by two +hexadecimal digits, in which case the hexadecimal number defines the code point +to match. By default, as in Perl, a hexadecimal number is always expected after +\x, but it may have zero, one, or two digits (so, for example, \xz matches a +binary zero character followed by z). +

+  PCRE_MULTILINE
+

+By default, for the purposes of matching "start of line" and "end of line", +PCRE treats the subject string as consisting of a single line of characters, +even if it actually contains newlines. The "start of line" metacharacter (^) +matches only at the start of the string, and the "end of line" metacharacter +($) matches only at the end of the string, or before a terminating newline +(except when PCRE_DOLLAR_ENDONLY is set). Note, however, that unless +PCRE_DOTALL is set, the "any character" metacharacter (.) does not match at a +newline. This behaviour (for ^, $, and dot) is the same as Perl. +

+When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs +match immediately following or immediately before internal newlines in the +subject string, respectively, as well as at the very start and end. This is +equivalent to Perl's /m option, and it can be changed within a pattern by a +(?m) option setting. If there are no newlines in a subject string, or no +occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect. +

+  PCRE_NEVER_UTF
+

+This option locks out interpretation of the pattern as UTF-8 (or UTF-16 or +UTF-32 in the 16-bit and 32-bit libraries). In particular, it prevents the +creator of the pattern from switching to UTF interpretation by starting the +pattern with (*UTF). This may be useful in applications that process patterns +from external sources. The combination of PCRE_UTF8 and PCRE_NEVER_UTF also +causes an error. +

+  PCRE_NEWLINE_CR
+  PCRE_NEWLINE_LF
+  PCRE_NEWLINE_CRLF
+  PCRE_NEWLINE_ANYCRLF
+  PCRE_NEWLINE_ANY
+

+These options override the default newline definition that was chosen when PCRE +was built. Setting the first or the second specifies that a newline is +indicated by a single character (CR or LF, respectively). Setting +PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character +CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three +preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies +that any Unicode newline sequence should be recognized. +

+In an ASCII/Unicode environment, the Unicode newline sequences are the three +just mentioned, plus the single characters VT (vertical tab, U+000B), FF (form +feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS +(paragraph separator, U+2029). For the 8-bit library, the last two are +recognized only in UTF-8 mode. +

+When PCRE is compiled to run in an EBCDIC (mainframe) environment, the code for +CR is 0x0d, the same as ASCII. However, the character code for LF is normally +0x15, though in some EBCDIC environments 0x25 is used. Whichever of these is +not LF is made to correspond to Unicode's NEL character. EBCDIC codes are all +less than 256. For more details, see the +pcrebuild +documentation. +

+The newline setting in the options word uses three bits that are treated +as a number, giving eight possibilities. Currently only six are used (default +plus the five values above). This means that if you set more than one newline +option, the combination may or may not be sensible. For example, +PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but +other combinations may yield unused numbers and cause an error. +

+The only time that a line break in a pattern is specially recognized when +compiling is when PCRE_EXTENDED is set. CR and LF are white space characters, +and so are ignored in this mode. Also, an unescaped # outside a character class +indicates a comment that lasts until after the next line break sequence. In +other circumstances, line break sequences in patterns are treated as literal +data. +

+The newline option that is set at compile time becomes the default that is used +for pcre_exec() and pcre_dfa_exec(), but it can be overridden. +

+  PCRE_NO_AUTO_CAPTURE
+

+If this option is set, it disables the use of numbered capturing parentheses in +the pattern. Any opening parenthesis that is not followed by ? behaves as if it +were followed by ?: but named parentheses can still be used for capturing (and +they acquire numbers in the usual way). There is no equivalent of this option +in Perl. +

+  PCRE_NO_AUTO_POSSESS
+

+If this option is set, it disables "auto-possessification". This is an +optimization that, for example, turns a+b into a++b in order to avoid +backtracks into a+ that can never be successful. However, if callouts are in +use, auto-possessification means that some of them are never taken. You can set +this option if you want the matching functions to do a full unoptimized search +and run all the callouts, but it is mainly provided for testing purposes. +

+  PCRE_NO_START_OPTIMIZE
+

+This is an option that acts at matching time; that is, it is really an option +for pcre_exec() or pcre_dfa_exec(). If it is set at compile time, +it is remembered with the compiled pattern and assumed at matching time. This +is necessary if you want to use JIT execution, because the JIT compiler needs +to know whether or not this option is set. For details see the discussion of +PCRE_NO_START_OPTIMIZE +below. +

+  PCRE_UCP
+

+This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W, +\w, and some of the POSIX character classes. By default, only ASCII characters +are recognized, but if PCRE_UCP is set, Unicode properties are used instead to +classify characters. More details are given in the section on +generic character types +in the +pcrepattern +page. If you set PCRE_UCP, matching one of the items it affects takes much +longer. The option is available only if PCRE has been compiled with Unicode +property support. +

+  PCRE_UNGREEDY
+

+This option inverts the "greediness" of the quantifiers so that they are not +greedy by default, but become greedy if followed by "?". It is not compatible +with Perl. It can also be set by a (?U) option setting within the pattern. +

+  PCRE_UTF8
+

+This option causes PCRE to regard both the pattern and the subject as strings +of UTF-8 characters instead of single-byte strings. However, it is available +only when PCRE is built to include UTF support. If not, the use of this option +provokes an error. Details of how this option changes the behaviour of PCRE are +given in the +pcreunicode +page. +

+  PCRE_NO_UTF8_CHECK
+

+When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is +automatically checked. There is a discussion about the +validity of UTF-8 strings +in the +pcreunicode +page. If an invalid UTF-8 sequence is found, pcre_compile() returns an +error. If you already know that your pattern is valid, and you want to skip +this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK option. +When it is set, the effect of passing an invalid UTF-8 string as a pattern is +undefined. It may cause your program to crash or loop. Note that this option +can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress +the validity checking of subject strings only. If the same string is being +matched many times, the option can be safely set for the second and subsequent +matchings to improve performance. +

+
COMPILATION ERROR CODES
+

+The following table lists the error codes than may be returned by +pcre_compile2(), along with the error messages that may be returned by +both compiling functions. Note that error messages are always 8-bit ASCII +strings, even in 16-bit or 32-bit mode. As PCRE has developed, some error codes +have fallen out of use. To avoid confusion, they have not been re-used. +

+   0  no error
+   1  \ at end of pattern
+   2  \c at end of pattern
+   3  unrecognized character follows \
+   4  numbers out of order in {} quantifier
+   5  number too big in {} quantifier
+   6  missing terminating ] for character class
+   7  invalid escape sequence in character class
+   8  range out of order in character class
+   9  nothing to repeat
+  10  [this code is not in use]
+  11  internal error: unexpected repeat
+  12  unrecognized character after (? or (?-
+  13  POSIX named classes are supported only within a class
+  14  missing )
+  15  reference to non-existent subpattern
+  16  erroffset passed as NULL
+  17  unknown option bit(s) set
+  18  missing ) after comment
+  19  [this code is not in use]
+  20  regular expression is too large
+  21  failed to get memory
+  22  unmatched parentheses
+  23  internal error: code overflow
+  24  unrecognized character after (?<
+  25  lookbehind assertion is not fixed length
+  26  malformed number or name after (?(
+  27  conditional group contains more than two branches
+  28  assertion expected after (?(
+  29  (?R or (?[+-]digits must be followed by )
+  30  unknown POSIX class name
+  31  POSIX collating elements are not supported
+  32  this version of PCRE is compiled without UTF support
+  33  [this code is not in use]
+  34  character value in \x{} or \o{} is too large
+  35  invalid condition (?(0)
+  36  \C not allowed in lookbehind assertion
+  37  PCRE does not support \L, \l, \N{name}, \U, or \u
+  38  number after (?C is > 255
+  39  closing ) for (?C expected
+  40  recursive call could loop indefinitely
+  41  unrecognized character after (?P
+  42  syntax error in subpattern name (missing terminator)
+  43  two named subpatterns have the same name
+  44  invalid UTF-8 string (specifically UTF-8)
+  45  support for \P, \p, and \X has not been compiled
+  46  malformed \P or \p sequence
+  47  unknown property name after \P or \p
+  48  subpattern name is too long (maximum 32 characters)
+  49  too many named subpatterns (maximum 10000)
+  50  [this code is not in use]
+  51  octal value is greater than \377 in 8-bit non-UTF-8 mode
+  52  internal error: overran compiling workspace
+  53  internal error: previously-checked referenced subpattern
+        not found
+  54  DEFINE group contains more than one branch
+  55  repeating a DEFINE group is not allowed
+  56  inconsistent NEWLINE options
+  57  \g is not followed by a braced, angle-bracketed, or quoted
+        name/number or by a plain number
+  58  a numbered reference must not be zero
+  59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
+  60  (*VERB) not recognized or malformed
+  61  number is too big
+  62  subpattern name expected
+  63  digit expected after (?+
+  64  ] is an invalid data character in JavaScript compatibility mode
+  65  different names for subpatterns of the same number are
+        not allowed
+  66  (*MARK) must have an argument
+  67  this version of PCRE is not compiled with Unicode property
+        support
+  68  \c must be followed by an ASCII character
+  69  \k is not followed by a braced, angle-bracketed, or quoted name
+  70  internal error: unknown opcode in find_fixedlength()
+  71  \N is not supported in a class
+  72  too many forward references
+  73  disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
+  74  invalid UTF-16 string (specifically UTF-16)
+  75  name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
+  76  character value in \u.... sequence is too large
+  77  invalid UTF-32 string (specifically UTF-32)
+  78  setting UTF is disabled by the application
+  79  non-hex character in \x{} (closing brace missing?)
+  80  non-octal character in \o{} (closing brace missing?)
+  81  missing opening brace after \o
+  82  parentheses are too deeply nested
+  83  invalid range in character class
+  84  group name must start with a non-digit
+  85  parentheses are too deeply nested (stack check)
+

+The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may +be used if the limits were changed when PCRE was built. +

+
STUDYING A PATTERN
+

+pcre_extra *pcre_study(const pcre *code, int options, + const char **errptr); +

+If a compiled pattern is going to be used several times, it is worth spending +more time analyzing it in order to speed up the time taken for matching. The +function pcre_study() takes a pointer to a compiled pattern as its first +argument. If studying the pattern produces additional information that will +help speed up matching, pcre_study() returns a pointer to a +pcre_extra block, in which the study_data field points to the +results of the study. +

+The returned value from pcre_study() can be passed directly to +pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block +also contains other fields that can be set by the caller before the block is +passed; these are described +below +in the section on matching a pattern. +

+If studying the pattern does not produce any useful information, +pcre_study() returns NULL by default. In that circumstance, if the +calling program wants to pass any of the other fields to pcre_exec() or +pcre_dfa_exec(), it must set up its own pcre_extra block. However, +if pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it +returns a pcre_extra block even if studying did not find any additional +information. It may still return NULL, however, if an error occurs in +pcre_study(). +

+The second argument of pcre_study() contains option bits. There are three +further options in addition to PCRE_STUDY_EXTRA_NEEDED: +

+  PCRE_STUDY_JIT_COMPILE
+  PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
+  PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
+

+If any of these are set, and the just-in-time compiler is available, the +pattern is further compiled into machine code that executes much faster than +the pcre_exec() interpretive matching function. If the just-in-time +compiler is not available, these options are ignored. All undefined bits in the +options argument must be zero. +

+JIT compilation is a heavyweight optimization. It can take some time for +patterns to be analyzed, and for one-off matches and simple patterns the +benefit of faster execution might be offset by a much slower study time. +Not all patterns can be optimized by the JIT compiler. For those that cannot be +handled, matching automatically falls back to the pcre_exec() +interpreter. For more details, see the +pcrejit +documentation. +

+The third argument for pcre_study() is a pointer for an error message. If +studying succeeds (even if no data is returned), the variable it points to is +set to NULL. Otherwise it is set to point to a textual error message. This is a +static string that is part of the library. You must not try to free it. You +should test the error pointer for NULL after calling pcre_study(), to be +sure that it has run successfully. +

+When you are finished with a pattern, you can free the memory used for the +study data by calling pcre_free_study(). This function was added to the +API for release 8.20. For earlier versions, the memory could be freed with +pcre_free(), just like the pattern itself. This will still work in cases +where JIT optimization is not used, but it is advisable to change to the new +function when convenient. +

+This is a typical way in which pcre_study() is used (except that in a +real application there should be tests for errors): +

+  int rc;
+  pcre *re;
+  pcre_extra *sd;
+  re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
+  sd = pcre_study(
+    re,             /* result of pcre_compile() */
+    0,              /* no options */
+    &error);        /* set to NULL or points to a message */
+  rc = pcre_exec(   /* see below for details of pcre_exec() options */
+    re, sd, "subject", 7, 0, 0, ovector, 30);
+  ...
+  pcre_free_study(sd);
+  pcre_free(re);
+

+Studying a pattern does two things: first, a lower bound for the length of +subject string that is needed to match the pattern is computed. This does not +mean that there are any strings of that length that match, but it does +guarantee that no shorter strings match. The value is used to avoid wasting +time by trying to match strings that are shorter than the lower bound. You can +find out the value in a calling program via the pcre_fullinfo() function. +

+Studying a pattern is also useful for non-anchored patterns that do not have a +single fixed starting character. A bitmap of possible starting bytes is +created. This speeds up finding a position in the subject at which to start +matching. (In 16-bit mode, the bitmap is used for 16-bit values less than 256. +In 32-bit mode, the bitmap is used for 32-bit values less than 256.) +

+These two optimizations apply to both pcre_exec() and +pcre_dfa_exec(), and the information is also used by the JIT compiler. +The optimizations can be disabled by setting the PCRE_NO_START_OPTIMIZE option. +You might want to do this if your pattern contains callouts or (*MARK) and you +want to make use of these facilities in cases where matching fails. +

+PCRE_NO_START_OPTIMIZE can be specified at either compile time or execution +time. However, if PCRE_NO_START_OPTIMIZE is passed to pcre_exec(), (that +is, after any JIT compilation has happened) JIT execution is disabled. For JIT +execution to work with PCRE_NO_START_OPTIMIZE, the option must be set at +compile time. +

+There is a longer discussion of PCRE_NO_START_OPTIMIZE +below. +

+
LOCALE SUPPORT
+

+PCRE handles caseless matching, and determines whether characters are letters, +digits, or whatever, by reference to a set of tables, indexed by character +code point. When running in UTF-8 mode, or in the 16- or 32-bit libraries, this +applies only to characters with code points less than 256. By default, +higher-valued code points never match escapes such as \w or \d. However, if +PCRE is built with Unicode property support, all characters can be tested with +\p and \P, or, alternatively, the PCRE_UCP option can be set when a pattern +is compiled; this causes \w and friends to use Unicode property support +instead of the built-in tables. +

+The use of locales with Unicode is discouraged. If you are handling characters +with code points greater than 128, you should either use Unicode support, or +use locales, but not try to mix the two. +

+PCRE contains an internal set of tables that are used when the final argument +of pcre_compile() is NULL. These are sufficient for many applications. +Normally, the internal tables recognize only ASCII characters. However, when +PCRE is built, it is possible to cause the internal tables to be rebuilt in the +default "C" locale of the local system, which may cause them to be different. +

+The internal tables can always be overridden by tables supplied by the +application that calls PCRE. These may be created in a different locale from +the default. As more and more applications change to using Unicode, the need +for this locale support is expected to die away. +

+External tables are built by calling the pcre_maketables() function, +which has no arguments, in the relevant locale. The result can then be passed +to pcre_compile() as often as necessary. For example, to build and use +tables that are appropriate for the French locale (where accented characters +with values greater than 128 are treated as letters), the following code could +be used: +

+  setlocale(LC_CTYPE, "fr_FR");
+  tables = pcre_maketables();
+  re = pcre_compile(..., tables);
+

+The locale name "fr_FR" is used on Linux and other Unix-like systems; if you +are using Windows, the name for the French locale is "french". +

+When pcre_maketables() runs, the tables are built in memory that is +obtained via pcre_malloc. It is the caller's responsibility to ensure +that the memory containing the tables remains available for as long as it is +needed. +

+The pointer that is passed to pcre_compile() is saved with the compiled +pattern, and the same tables are used via this pointer by pcre_study() +and also by pcre_exec() and pcre_dfa_exec(). Thus, for any single +pattern, compilation, studying and matching all happen in the same locale, but +different patterns can be processed in different locales. +

+It is possible to pass a table pointer or NULL (indicating the use of the +internal tables) to pcre_exec() or pcre_dfa_exec() (see the +discussion below in the section on matching a pattern). This facility is +provided for use with pre-compiled patterns that have been saved and reloaded. +Character tables are not saved with patterns, so if a non-standard table was +used at compile time, it must be provided again when the reloaded pattern is +matched. Attempting to use this facility to match a pattern in a different +locale from the one in which it was compiled is likely to lead to anomalous +(usually incorrect) results. +

+
INFORMATION ABOUT A PATTERN
+

+int pcre_fullinfo(const pcre *code, const pcre_extra *extra, + int what, void *where); +

+The pcre_fullinfo() function returns information about a compiled +pattern. It replaces the pcre_info() function, which was removed from the +library at version 8.30, after more than 10 years of obsolescence. +

+The first argument for pcre_fullinfo() is a pointer to the compiled +pattern. The second argument is the result of pcre_study(), or NULL if +the pattern was not studied. The third argument specifies which piece of +information is required, and the fourth argument is a pointer to a variable +to receive the data. The yield of the function is zero for success, or one of +the following negative numbers: +

+  PCRE_ERROR_NULL           the argument code was NULL
+                            the argument where was NULL
+  PCRE_ERROR_BADMAGIC       the "magic number" was not found
+  PCRE_ERROR_BADENDIANNESS  the pattern was compiled with different
+                            endianness
+  PCRE_ERROR_BADOPTION      the value of what was invalid
+  PCRE_ERROR_UNSET          the requested field is not set
+

+The "magic number" is placed at the start of each compiled pattern as an simple +check against passing an arbitrary memory pointer. The endianness error can +occur if a compiled pattern is saved and reloaded on a different host. Here is +a typical call of pcre_fullinfo(), to obtain the length of the compiled +pattern: +

+  int rc;
+  size_t length;
+  rc = pcre_fullinfo(
+    re,               /* result of pcre_compile() */
+    sd,               /* result of pcre_study(), or NULL */
+    PCRE_INFO_SIZE,   /* what is required */
+    &length);         /* where to put the data */
+

+The possible values for the third argument are defined in pcre.h, and are +as follows: +

+  PCRE_INFO_BACKREFMAX
+

+Return the number of the highest back reference in the pattern. The fourth +argument should point to an int variable. Zero is returned if there are +no back references. +

+  PCRE_INFO_CAPTURECOUNT
+

+Return the number of capturing subpatterns in the pattern. The fourth argument +should point to an int variable. +

+  PCRE_INFO_DEFAULT_TABLES
+

+Return a pointer to the internal default character tables within PCRE. The +fourth argument should point to an unsigned char * variable. This +information call is provided for internal use by the pcre_study() +function. External callers can cause PCRE to use its internal tables by passing +a NULL table pointer. +

+  PCRE_INFO_FIRSTBYTE (deprecated)
+

+Return information about the first data unit of any matched string, for a +non-anchored pattern. The name of this option refers to the 8-bit library, +where data units are bytes. The fourth argument should point to an int +variable. Negative values are used for special cases. However, this means that +when the 32-bit library is in non-UTF-32 mode, the full 32-bit range of +characters cannot be returned. For this reason, this value is deprecated; use +PCRE_INFO_FIRSTCHARACTERFLAGS and PCRE_INFO_FIRSTCHARACTER instead. +

+If there is a fixed first value, for example, the letter "c" from a pattern +such as (cat|cow|coyote), its value is returned. In the 8-bit library, the +value is always less than 256. In the 16-bit library the value can be up to +0xffff. In the 32-bit library the value can be up to 0x10ffff. +

+If there is no fixed first value, and if either +
+
+(a) the pattern was compiled with the PCRE_MULTILINE option, and every branch +starts with "^", or +
+
+(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set +(if it were set, the pattern would be anchored), +
+
+-1 is returned, indicating that the pattern matches only at the start of a +subject string or after any newline within the string. Otherwise -2 is +returned. For anchored patterns, -2 is returned. +

+  PCRE_INFO_FIRSTCHARACTER
+

+Return the value of the first data unit (non-UTF character) of any matched +string in the situation where PCRE_INFO_FIRSTCHARACTERFLAGS returns 1; +otherwise return 0. The fourth argument should point to an uint_t +variable. +

+In the 8-bit library, the value is always less than 256. In the 16-bit library +the value can be up to 0xffff. In the 32-bit library in UTF-32 mode the value +can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32 mode. +

+  PCRE_INFO_FIRSTCHARACTERFLAGS
+

+Return information about the first data unit of any matched string, for a +non-anchored pattern. The fourth argument should point to an int +variable. +

+If there is a fixed first value, for example, the letter "c" from a pattern +such as (cat|cow|coyote), 1 is returned, and the character value can be +retrieved using PCRE_INFO_FIRSTCHARACTER. If there is no fixed first value, and +if either +
+
+(a) the pattern was compiled with the PCRE_MULTILINE option, and every branch +starts with "^", or +
+
+(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set +(if it were set, the pattern would be anchored), +
+
+2 is returned, indicating that the pattern matches only at the start of a +subject string or after any newline within the string. Otherwise 0 is +returned. For anchored patterns, 0 is returned. +

+  PCRE_INFO_FIRSTTABLE
+

+If the pattern was studied, and this resulted in the construction of a 256-bit +table indicating a fixed set of values for the first data unit in any matching +string, a pointer to the table is returned. Otherwise NULL is returned. The +fourth argument should point to an unsigned char * variable. +

+  PCRE_INFO_HASCRORLF
+

+Return 1 if the pattern contains any explicit matches for CR or LF characters, +otherwise 0. The fourth argument should point to an int variable. An +explicit match is either a literal CR or LF character, or \r or \n. +

+  PCRE_INFO_JCHANGED
+

+Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise +0. The fourth argument should point to an int variable. (?J) and +(?-J) set and unset the local PCRE_DUPNAMES option, respectively. +

+  PCRE_INFO_JIT
+

+Return 1 if the pattern was studied with one of the JIT options, and +just-in-time compiling was successful. The fourth argument should point to an +int variable. A return value of 0 means that JIT support is not available +in this version of PCRE, or that the pattern was not studied with a JIT option, +or that the JIT compiler could not handle this particular pattern. See the +pcrejit +documentation for details of what can and cannot be handled. +

+  PCRE_INFO_JITSIZE
+

+If the pattern was successfully studied with a JIT option, return the size of +the JIT compiled code, otherwise return zero. The fourth argument should point +to a size_t variable. +

+  PCRE_INFO_LASTLITERAL
+

+Return the value of the rightmost literal data unit that must exist in any +matched string, other than at its start, if such a value has been recorded. The +fourth argument should point to an int variable. If there is no such +value, -1 is returned. For anchored patterns, a last literal value is recorded +only if it follows something of variable length. For example, for the pattern +/^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value +is -1. +

+Since for the 32-bit library using the non-UTF-32 mode, this function is unable +to return the full 32-bit range of characters, this value is deprecated; +instead the PCRE_INFO_REQUIREDCHARFLAGS and PCRE_INFO_REQUIREDCHAR values should +be used. +

+  PCRE_INFO_MATCH_EMPTY
+

+Return 1 if the pattern can match an empty string, otherwise 0. The fourth +argument should point to an int variable. +

+  PCRE_INFO_MATCHLIMIT
+

+If the pattern set a match limit by including an item of the form +(*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth argument +should point to an unsigned 32-bit integer. If no such value has been set, the +call to pcre_fullinfo() returns the error PCRE_ERROR_UNSET. +

+  PCRE_INFO_MAXLOOKBEHIND
+

+Return the number of characters (NB not data units) in the longest lookbehind +assertion in the pattern. This information is useful when doing multi-segment +matching using the partial matching facilities. Note that the simple assertions +\b and \B require a one-character lookbehind. \A also registers a +one-character lookbehind, though it does not actually inspect the previous +character. This is to ensure that at least one character from the old segment +is retained when a new segment is processed. Otherwise, if there are no +lookbehinds in the pattern, \A might match incorrectly at the start of a new +segment. +

+  PCRE_INFO_MINLENGTH
+

+If the pattern was studied and a minimum length for matching subject strings +was computed, its value is returned. Otherwise the returned value is -1. The +value is a number of characters, which in UTF mode may be different from the +number of data units. The fourth argument should point to an int +variable. A non-negative value is a lower bound to the length of any matching +string. There may not be any strings of that length that do actually match, but +every string that does match is at least that long. +

+  PCRE_INFO_NAMECOUNT
+  PCRE_INFO_NAMEENTRYSIZE
+  PCRE_INFO_NAMETABLE
+

+PCRE supports the use of named as well as numbered capturing parentheses. The +names are just an additional way of identifying the parentheses, which still +acquire numbers. Several convenience functions such as +pcre_get_named_substring() are provided for extracting captured +substrings by name. It is also possible to extract the data directly, by first +converting the name to a number in order to access the correct pointers in the +output vector (described with pcre_exec() below). To do the conversion, +you need to use the name-to-number map, which is described by these three +values. +

+The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives +the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each +entry; both of these return an int value. The entry size depends on the +length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first +entry of the table. This is a pointer to char in the 8-bit library, where +the first two bytes of each entry are the number of the capturing parenthesis, +most significant byte first. In the 16-bit library, the pointer points to +16-bit data units, the first of which contains the parenthesis number. In the +32-bit library, the pointer points to 32-bit data units, the first of which +contains the parenthesis number. The rest of the entry is the corresponding +name, zero terminated. +

+The names are in alphabetical order. If (?| is used to create multiple groups +with the same number, as described in the +section on duplicate subpattern numbers +in the +pcrepattern +page, the groups may be given the same name, but there is only one entry in the +table. Different names for groups of the same number are not permitted. +Duplicate names for subpatterns with different numbers are permitted, +but only if PCRE_DUPNAMES is set. They appear in the table in the order in +which they were found in the pattern. In the absence of (?| this is the order +of increasing number; when (?| is used this is not necessarily the case because +later subpatterns may have lower numbers. +

+As a simple example of the name/number table, consider the following pattern +after compilation by the 8-bit library (assume PCRE_EXTENDED is set, so white +space - including newlines - is ignored): +

+  (?<date> (?<year>(\d\d)?\d\d) - (?<month>\d\d) - (?<day>\d\d) )
+

+There are four named subpatterns, so the table has four entries, and each entry +in the table is eight bytes long. The table is as follows, with non-printing +bytes shows in hexadecimal, and undefined bytes shown as ??: +

+  00 01 d  a  t  e  00 ??
+  00 05 d  a  y  00 ?? ??
+  00 04 m  o  n  t  h  00
+  00 02 y  e  a  r  00 ??
+

+When writing code to extract data from named subpatterns using the +name-to-number map, remember that the length of the entries is likely to be +different for each compiled pattern. +

+  PCRE_INFO_OKPARTIAL
+

+Return 1 if the pattern can be used for partial matching with +pcre_exec(), otherwise 0. The fourth argument should point to an +int variable. From release 8.00, this always returns 1, because the +restrictions that previously applied to partial matching have been lifted. The +pcrepartial +documentation gives details of partial matching. +

+  PCRE_INFO_OPTIONS
+

+Return a copy of the options with which the pattern was compiled. The fourth +argument should point to an unsigned long int variable. These option bits +are those specified in the call to pcre_compile(), modified by any +top-level option settings at the start of the pattern itself. In other words, +they are the options that will be in force when matching starts. For example, +if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the +result is PCRE_CASELESS, PCRE_MULTILINE, and PCRE_EXTENDED. +

+A pattern is automatically anchored by PCRE if all of its top-level +alternatives begin with one of the following: +

+  ^     unless PCRE_MULTILINE is set
+  \A    always
+  \G    always
+  .*    if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
+

+For such patterns, the PCRE_ANCHORED bit is set in the options returned by +pcre_fullinfo(). +

+  PCRE_INFO_RECURSIONLIMIT
+

+If the pattern set a recursion limit by including an item of the form +(*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth +argument should point to an unsigned 32-bit integer. If no such value has been +set, the call to pcre_fullinfo() returns the error PCRE_ERROR_UNSET. +

+  PCRE_INFO_SIZE
+

+Return the size of the compiled pattern in bytes (for all three libraries). The +fourth argument should point to a size_t variable. This value does not +include the size of the pcre structure that is returned by +pcre_compile(). The value that is passed as the argument to +pcre_malloc() when pcre_compile() is getting memory in which to +place the compiled data is the value returned by this option plus the size of +the pcre structure. Studying a compiled pattern, with or without JIT, +does not alter the value returned by this option. +

+  PCRE_INFO_STUDYSIZE
+

+Return the size in bytes (for all three libraries) of the data block pointed to +by the study_data field in a pcre_extra block. If pcre_extra +is NULL, or there is no study data, zero is returned. The fourth argument +should point to a size_t variable. The study_data field is set by +pcre_study() to record information that will speed up matching (see the +section entitled +"Studying a pattern" +above). The format of the study_data block is private, but its length +is made available via this option so that it can be saved and restored (see the +pcreprecompile +documentation for details). +

+  PCRE_INFO_REQUIREDCHARFLAGS
+

+Returns 1 if there is a rightmost literal data unit that must exist in any +matched string, other than at its start. The fourth argument should point to +an int variable. If there is no such value, 0 is returned. If returning +1, the character value itself can be retrieved using PCRE_INFO_REQUIREDCHAR. +

+For anchored patterns, a last literal value is recorded only if it follows +something of variable length. For example, for the pattern /^a\d+z\d+/ the +returned value 1 (with "z" returned from PCRE_INFO_REQUIREDCHAR), but for +/^a\dz\d/ the returned value is 0. +

+  PCRE_INFO_REQUIREDCHAR
+

+
REFERENCE COUNTS
+

+int pcre_refcount(pcre *code, int adjust); +

+The pcre_refcount() function is used to maintain a reference count in the +data block that contains a compiled pattern. It is provided for the benefit of +applications that operate in an object-oriented manner, where different parts +of the application may be using the same compiled pattern, but you want to free +the block when they are all done. +

+When a pattern is compiled, the reference count field is initialized to zero. +It is changed only by calling this function, whose action is to add the +adjust value (which may be positive or negative) to it. The yield of the +function is the new value. However, the value of the count is constrained to +lie between 0 and 65535, inclusive. If the new value is outside these limits, +it is forced to the appropriate limit value. +

+Except when it is zero, the reference count is not correctly preserved if a +pattern is compiled on one host and then transferred to a host whose byte-order +is different. (This seems a highly unlikely scenario.) +

+
MATCHING A PATTERN: THE TRADITIONAL FUNCTION
+

+int pcre_exec(const pcre *code, const pcre_extra *extra, + const char *subject, int length, int startoffset, + int options, int *ovector, int ovecsize); +

+The function pcre_exec() is called to match a subject string against a +compiled pattern, which is passed in the code argument. If the +pattern was studied, the result of the study should be passed in the +extra argument. You can call pcre_exec() with the same code +and extra arguments as many times as you like, in order to match +different subject strings with the same pattern. +

+This function is the main matching facility of the library, and it operates in +a Perl-like manner. For specialist use there is also an alternative matching +function, which is described +below +in the section about the pcre_dfa_exec() function. +

+In most applications, the pattern will have been compiled (and optionally +studied) in the same process that calls pcre_exec(). However, it is +possible to save compiled patterns and study data, and then use them later +in different processes, possibly even on different hosts. For a discussion +about this, see the +pcreprecompile +documentation. +

+Here is an example of a simple call to pcre_exec(): +

+  int rc;
+  int ovector[30];
+  rc = pcre_exec(
+    re,             /* result of pcre_compile() */
+    NULL,           /* we didn't study the pattern */
+    "some string",  /* the subject string */
+    11,             /* the length of the subject string */
+    0,              /* start at offset 0 in the subject */
+    0,              /* default options */
+    ovector,        /* vector of integers for substring information */
+    30);            /* number of elements (NOT size in bytes) */
+

+
+Extra data for pcre_exec() +
+

+If the extra argument is not NULL, it must point to a pcre_extra +data block. The pcre_study() function returns such a block (when it +doesn't return NULL), but you can also create one for yourself, and pass +additional information in it. The pcre_extra block contains the following +fields (not necessarily in this order): +

+  unsigned long int flags;
+  void *study_data;
+  void *executable_jit;
+  unsigned long int match_limit;
+  unsigned long int match_limit_recursion;
+  void *callout_data;
+  const unsigned char *tables;
+  unsigned char **mark;
+

+In the 16-bit version of this structure, the mark field has type +"PCRE_UCHAR16 **". +
+
+In the 32-bit version of this structure, the mark field has type +"PCRE_UCHAR32 **". +

+The flags field is used to specify which of the other fields are set. The +flag bits are: +

+  PCRE_EXTRA_CALLOUT_DATA
+  PCRE_EXTRA_EXECUTABLE_JIT
+  PCRE_EXTRA_MARK
+  PCRE_EXTRA_MATCH_LIMIT
+  PCRE_EXTRA_MATCH_LIMIT_RECURSION
+  PCRE_EXTRA_STUDY_DATA
+  PCRE_EXTRA_TABLES
+

+Other flag bits should be set to zero. The study_data field and sometimes +the executable_jit field are set in the pcre_extra block that is +returned by pcre_study(), together with the appropriate flag bits. You +should not set these yourself, but you may add to the block by setting other +fields and their corresponding flag bits. +

+The match_limit field provides a means of preventing PCRE from using up a +vast amount of resources when running patterns that are not going to match, +but which have a very large number of possibilities in their search trees. The +classic example is a pattern that uses nested unlimited repeats. +

+Internally, pcre_exec() uses a function called match(), which it +calls repeatedly (sometimes recursively). The limit set by match_limit is +imposed on the number of times this function is called during a match, which +has the effect of limiting the amount of backtracking that can take place. For +patterns that are not anchored, the count restarts from zero for each position +in the subject string. +

+When pcre_exec() is called with a pattern that was successfully studied +with a JIT option, the way that the matching is executed is entirely different. +However, there is still the possibility of runaway matching that goes on for a +very long time, and so the match_limit value is also used in this case +(but in a different way) to limit how long the matching can continue. +

+The default value for the limit can be set when PCRE is built; the default +default is 10 million, which handles all but the most extreme cases. You can +override the default by suppling pcre_exec() with a pcre_extra +block in which match_limit is set, and PCRE_EXTRA_MATCH_LIMIT is set in +the flags field. If the limit is exceeded, pcre_exec() returns +PCRE_ERROR_MATCHLIMIT. +

+A value for the match limit may also be supplied by an item at the start of a +pattern of the form +

+  (*LIMIT_MATCH=d)
+

+where d is a decimal number. However, such a setting is ignored unless d is +less than the limit set by the caller of pcre_exec() or, if no such limit +is set, less than the default. +

+The match_limit_recursion field is similar to match_limit, but +instead of limiting the total number of times that match() is called, it +limits the depth of recursion. The recursion depth is a smaller number than the +total number of calls, because not all calls to match() are recursive. +This limit is of use only if it is set smaller than match_limit. +

+Limiting the recursion depth limits the amount of machine stack that can be +used, or, when PCRE has been compiled to use memory on the heap instead of the +stack, the amount of heap memory that can be used. This limit is not relevant, +and is ignored, when matching is done using JIT compiled code. +

+The default value for match_limit_recursion can be set when PCRE is +built; the default default is the same value as the default for +match_limit. You can override the default by suppling pcre_exec() +with a pcre_extra block in which match_limit_recursion is set, and +PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the limit +is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT. +

+A value for the recursion limit may also be supplied by an item at the start of +a pattern of the form +

+  (*LIMIT_RECURSION=d)
+

+where d is a decimal number. However, such a setting is ignored unless d is +less than the limit set by the caller of pcre_exec() or, if no such limit +is set, less than the default. +

+The callout_data field is used in conjunction with the "callout" feature, +and is described in the +pcrecallout +documentation. +

+The tables field is provided for use with patterns that have been +pre-compiled using custom character tables, saved to disc or elsewhere, and +then reloaded, because the tables that were used to compile a pattern are not +saved with it. See the +pcreprecompile +documentation for a discussion of saving compiled patterns for later use. If +NULL is passed using this mechanism, it forces PCRE's internal tables to be +used. +

+Warning: The tables that pcre_exec() uses must be the same as those +that were used when the pattern was compiled. If this is not the case, the +behaviour of pcre_exec() is undefined. Therefore, when a pattern is +compiled and matched in the same process, this field should never be set. In +this (the most common) case, the correct table pointer is automatically passed +with the compiled pattern from pcre_compile() to pcre_exec(). +

+If PCRE_EXTRA_MARK is set in the flags field, the mark field must +be set to point to a suitable variable. If the pattern contains any +backtracking control verbs such as (*MARK:NAME), and the execution ends up with +a name to pass back, a pointer to the name string (zero terminated) is placed +in the variable pointed to by the mark field. The names are within the +compiled pattern; if you wish to retain such a name you must copy it before +freeing the memory of a compiled pattern. If there is no name to pass back, the +variable pointed to by the mark field is set to NULL. For details of the +backtracking control verbs, see the section entitled +"Backtracking control" +in the +pcrepattern +documentation. +

+
+Option bits for pcre_exec() +
+

+The unused bits of the options argument for pcre_exec() must be +zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx, +PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, +PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and +PCRE_PARTIAL_SOFT. +

+If the pattern was successfully studied with one of the just-in-time (JIT) +compile options, the only supported options for JIT execution are +PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, +PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an +unsupported option is used, JIT execution is disabled and the normal +interpretive code in pcre_exec() is run. +

+  PCRE_ANCHORED
+

+The PCRE_ANCHORED option limits pcre_exec() to matching at the first +matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out +to be anchored by virtue of its contents, it cannot be made unachored at +matching time. +

+  PCRE_BSR_ANYCRLF
+  PCRE_BSR_UNICODE
+

+These options (which are mutually exclusive) control what the \R escape +sequence matches. The choice is either to match only CR, LF, or CRLF, or to +match any Unicode newline sequence. These options override the choice that was +made or defaulted when the pattern was compiled. +

+  PCRE_NEWLINE_CR
+  PCRE_NEWLINE_LF
+  PCRE_NEWLINE_CRLF
+  PCRE_NEWLINE_ANYCRLF
+  PCRE_NEWLINE_ANY
+

+These options override the newline definition that was chosen or defaulted when +the pattern was compiled. For details, see the description of +pcre_compile() above. During matching, the newline choice affects the +behaviour of the dot, circumflex, and dollar metacharacters. It may also alter +the way the match position is advanced after a match failure for an unanchored +pattern. +

+When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a +match attempt for an unanchored pattern fails when the current position is at a +CRLF sequence, and the pattern contains no explicit matches for CR or LF +characters, the match position is advanced by two characters instead of one, in +other words, to after the CRLF. +

+The above rule is a compromise that makes the most common cases work as +expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not +set), it does not match the string "\r\nA" because, after failing at the +start, it skips both the CR and the LF before retrying. However, the pattern +[\r\n]A does match that string, because it contains an explicit CR or LF +reference, and so advances only by one character after the first failure. +

+An explicit match for CR of LF is either a literal appearance of one of those +characters, or one of the \r or \n escape sequences. Implicit matches such as +[^X] do not count, nor does \s (which includes CR and LF in the characters +that it matches). +

+Notwithstanding the above, anomalous effects may still occur when CRLF is a +valid newline sequence and explicit \r or \n escapes appear in the pattern. +

+  PCRE_NOTBOL
+

+This option specifies that first character of the subject string is not the +beginning of a line, so the circumflex metacharacter should not match before +it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex +never to match. This option affects only the behaviour of the circumflex +metacharacter. It does not affect \A. +

+  PCRE_NOTEOL
+

+This option specifies that the end of the subject string is not the end of a +line, so the dollar metacharacter should not match it nor (except in multiline +mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at +compile time) causes dollar never to match. This option affects only the +behaviour of the dollar metacharacter. It does not affect \Z or \z. +

+  PCRE_NOTEMPTY
+

+An empty string is not considered to be a valid match if this option is set. If +there are alternatives in the pattern, they are tried. If all the alternatives +match the empty string, the entire match fails. For example, if the pattern +

+  a?b?
+

+is applied to a string not beginning with "a" or "b", it matches an empty +string at the start of the subject. With PCRE_NOTEMPTY set, this match is not +valid, so PCRE searches further into the string for occurrences of "a" or "b". +

+  PCRE_NOTEMPTY_ATSTART
+

+This is like PCRE_NOTEMPTY, except that an empty string match that is not at +the start of the subject is permitted. If the pattern is anchored, such a match +can occur only if the pattern contains \K. +

+Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it +does make a special case of a pattern match of the empty string within its +split() function, and when using the /g modifier. It is possible to +emulate Perl's behaviour after matching a null string by first trying the match +again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then +if that fails, by advancing the starting offset (see below) and trying an +ordinary match again. There is some code that demonstrates how to do this in +the +pcredemo +sample program. In the most general case, you have to check to see if the +newline convention recognizes CRLF as a newline, and if so, and the current +character is CR followed by LF, advance the starting offset by two characters +instead of one. +

+  PCRE_NO_START_OPTIMIZE
+

+There are a number of optimizations that pcre_exec() uses at the start of +a match, in order to speed up the process. For example, if it is known that an +unanchored match must start with a specific character, it searches the subject +for that character, and fails immediately if it cannot find it, without +actually running the main matching function. This means that a special item +such as (*COMMIT) at the start of a pattern is not considered until after a +suitable starting point for the match has been found. Also, when callouts or +(*MARK) items are in use, these "start-up" optimizations can cause them to be +skipped if the pattern is never actually used. The start-up optimizations are +in effect a pre-scan of the subject that takes place before the pattern is run. +

+The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly +causing performance to suffer, but ensuring that in cases where the result is +"no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK) +are considered at every possible starting position in the subject string. If +PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching +time. The use of PCRE_NO_START_OPTIMIZE at matching time (that is, passing it +to pcre_exec()) disables JIT execution; in this situation, matching is +always done using interpretively. +

+Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation. +Consider the pattern +

+  (*COMMIT)ABC
+

+When this is compiled, PCRE records the fact that a match must start with the +character "A". Suppose the subject string is "DEFABC". The start-up +optimization scans along the subject, finds "A" and runs the first match +attempt from there. The (*COMMIT) item means that the pattern must match the +current starting position, which in this case, it does. However, if the same +match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the +subject string does not happen. The first match attempt is run starting from +"D" and when this fails, (*COMMIT) prevents any further matches being tried, so +the overall result is "no match". If the pattern is studied, more start-up +optimizations may be used. For example, a minimum length for the subject may be +recorded. Consider the pattern +

+  (*MARK:A)(X|Y)
+

+The minimum length for a match is one character. If the subject is "ABC", there +will be attempts to match "ABC", "BC", "C", and then finally an empty string. +If the pattern is studied, the final attempt does not take place, because PCRE +knows that the subject is too short, and so the (*MARK) is never encountered. +In this case, studying the pattern does not affect the overall match result, +which is still "no match", but it does affect the auxiliary information that is +returned. +

+  PCRE_NO_UTF8_CHECK
+

+When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8 +string is automatically checked when pcre_exec() is subsequently called. +The entire string is checked before any other processing takes place. The value +of startoffset is also checked to ensure that it points to the start of a +UTF-8 character. There is a discussion about the +validity of UTF-8 strings +in the +pcreunicode +page. If an invalid sequence of bytes is found, pcre_exec() returns the +error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a +truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In both +cases, information about the precise nature of the error may also be returned +(see the descriptions of these errors in the section entitled \fIError return +values from\fP pcre_exec() +below). +If startoffset contains a value that does not point to the start of a +UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is +returned. +

+If you already know that your subject is valid, and you want to skip these +checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when +calling pcre_exec(). You might want to do this for the second and +subsequent calls to pcre_exec() if you are making repeated calls to find +all the matches in a single subject string. However, you should be sure that +the value of startoffset points to the start of a character (or the end +of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an +invalid string as a subject or an invalid value of startoffset is +undefined. Your program may crash or loop. +

+  PCRE_PARTIAL_HARD
+  PCRE_PARTIAL_SOFT
+

+These options turn on the partial matching feature. For backwards +compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match +occurs if the end of the subject string is reached successfully, but there are +not enough subject characters to complete the match. If this happens when +PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by +testing any remaining alternatives. Only if no complete match can be found is +PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words, +PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match, +but only if no complete match can be found. +

+If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a +partial match is found, pcre_exec() immediately returns +PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words, +when PCRE_PARTIAL_HARD is set, a partial match is considered to be more +important that an alternative complete match. +

+In both cases, the portion of the string that was inspected when the partial +match was found is set as the first matching string. There is a more detailed +discussion of partial and multi-segment matching, with examples, in the +pcrepartial +documentation. +

+
+The string to be matched by pcre_exec() +
+

+The subject string is passed to pcre_exec() as a pointer in +subject, a length in length, and a starting offset in +startoffset. The units for length and startoffset are bytes +for the 8-bit library, 16-bit data items for the 16-bit library, and 32-bit +data items for the 32-bit library. +

+If startoffset is negative or greater than the length of the subject, +pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is +zero, the search for a match starts at the beginning of the subject, and this +is by far the most common case. In UTF-8 or UTF-16 mode, the offset must point +to the start of a character, or the end of the subject (in UTF-32 mode, one +data unit equals one character, so all offsets are valid). Unlike the pattern +string, the subject may contain binary zeroes. +

+A non-zero starting offset is useful when searching for another match in the +same subject by calling pcre_exec() again after a previous success. +Setting startoffset differs from just passing over a shortened string and +setting PCRE_NOTBOL in the case of a pattern that begins with any kind of +lookbehind. For example, consider the pattern +

+  \Biss\B
+

+which finds occurrences of "iss" in the middle of words. (\B matches only if +the current position in the subject is not a word boundary.) When applied to +the string "Mississipi" the first call to pcre_exec() finds the first +occurrence. If pcre_exec() is called again with just the remainder of the +subject, namely "issipi", it does not match, because \B is always false at the +start of the subject, which is deemed to be a word boundary. However, if +pcre_exec() is passed the entire string again, but with startoffset +set to 4, it finds the second occurrence of "iss" because it is able to look +behind the starting point to discover that it is preceded by a letter. +

+Finding all the matches in a subject is tricky when the pattern can match an +empty string. It is possible to emulate Perl's /g behaviour by first trying the +match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and +PCRE_ANCHORED options, and then if that fails, advancing the starting offset +and trying an ordinary match again. There is some code that demonstrates how to +do this in the +pcredemo +sample program. In the most general case, you have to check to see if the +newline convention recognizes CRLF as a newline, and if so, and the current +character is CR followed by LF, advance the starting offset by two characters +instead of one. +

+If a non-zero starting offset is passed when the pattern is anchored, one +attempt to match at the given offset is made. This can only succeed if the +pattern does not require the match to be at the start of the subject. +

+
+How pcre_exec() returns captured substrings +
+

+In general, a pattern matches a certain portion of the subject, and in +addition, further substrings from the subject may be picked out by parts of the +pattern. Following the usage in Jeffrey Friedl's book, this is called +"capturing" in what follows, and the phrase "capturing subpattern" is used for +a fragment of a pattern that picks out a substring. PCRE supports several other +kinds of parenthesized subpattern that do not cause substrings to be captured. +

+Captured substrings are returned to the caller via a vector of integers whose +address is passed in ovector. The number of elements in the vector is +passed in ovecsize, which must be a non-negative number. Note: this +argument is NOT the size of ovector in bytes. +

+The first two-thirds of the vector is used to pass back captured substrings, +each substring using a pair of integers. The remaining third of the vector is +used as workspace by pcre_exec() while matching capturing subpatterns, +and is not available for passing back information. The number passed in +ovecsize should always be a multiple of three. If it is not, it is +rounded down. +

+When a match is successful, information about captured substrings is returned +in pairs of integers, starting at the beginning of ovector, and +continuing up to two-thirds of its length at the most. The first element of +each pair is set to the offset of the first character in a substring, and the +second is set to the offset of the first character after the end of a +substring. These values are always data unit offsets, even in UTF mode. They +are byte offsets in the 8-bit library, 16-bit data item offsets in the 16-bit +library, and 32-bit data item offsets in the 32-bit library. Note: they +are not character counts. +

+The first pair of integers, ovector[0] and ovector[1], identify the +portion of the subject string matched by the entire pattern. The next pair is +used for the first capturing subpattern, and so on. The value returned by +pcre_exec() is one more than the highest numbered pair that has been set. +For example, if two substrings have been captured, the returned value is 3. If +there are no capturing subpatterns, the return value from a successful match is +1, indicating that just the first pair of offsets has been set. +

+If a capturing subpattern is matched repeatedly, it is the last portion of the +string that it matched that is returned. +

+If the vector is too small to hold all the captured substring offsets, it is +used as far as possible (up to two-thirds of its length), and the function +returns a value of zero. If neither the actual string matched nor any captured +substrings are of interest, pcre_exec() may be called with ovector +passed as NULL and ovecsize as zero. However, if the pattern contains +back references and the ovector is not big enough to remember the related +substrings, PCRE has to get additional memory for use during matching. Thus it +is usually advisable to supply an ovector of reasonable size. +

+There are some cases where zero is returned (indicating vector overflow) when +in fact the vector is exactly the right size for the final match. For example, +consider the pattern +

+  (a)(?:(b)c|bd)
+

+If a vector of 6 elements (allowing for only 1 captured substring) is given +with subject string "abd", pcre_exec() will try to set the second +captured string, thereby recording a vector overflow, before failing to match +"c" and backing up to try the second alternative. The zero return, however, +does correctly indicate that the maximum number of slots (namely 2) have been +filled. In similar cases where there is temporary overflow, but the final +number of used slots is actually less than the maximum, a non-zero value is +returned. +

+The pcre_fullinfo() function can be used to find out how many capturing +subpatterns there are in a compiled pattern. The smallest size for +ovector that will allow for n captured substrings, in addition to +the offsets of the substring matched by the whole pattern, is (n+1)*3. +

+It is possible for capturing subpattern number n+1 to match some part of +the subject when subpattern n has not been used at all. For example, if +the string "abc" is matched against the pattern (a|(z))(bc) the return from the +function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this +happens, both values in the offset pairs corresponding to unused subpatterns +are set to -1. +

+Offset values that correspond to unused subpatterns at the end of the +expression are also set to -1. For example, if the string "abc" is matched +against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The +return from the function is 2, because the highest used capturing subpattern +number is 1, and the offsets for for the second and third capturing subpatterns +(assuming the vector is large enough, of course) are set to -1. +

+Note: Elements in the first two-thirds of ovector that do not +correspond to capturing parentheses in the pattern are never changed. That is, +if a pattern contains n capturing parentheses, no more than +ovector[0] to ovector[2n+1] are set by pcre_exec(). The other +elements (in the first two-thirds) retain whatever values they previously had. +

+Some convenience functions are provided for extracting the captured substrings +as separate strings. These are described below. +

+
+Error return values from pcre_exec() +
+

+If pcre_exec() fails, it returns a negative number. The following are +defined in the header file: +

+  PCRE_ERROR_NOMATCH        (-1)
+

+The subject string did not match the pattern. +

+  PCRE_ERROR_NULL           (-2)
+

+Either code or subject was passed as NULL, or ovector was +NULL and ovecsize was not zero. +

+  PCRE_ERROR_BADOPTION      (-3)
+

+An unrecognized bit was set in the options argument. +

+  PCRE_ERROR_BADMAGIC       (-4)
+

+PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch +the case when it is passed a junk pointer and to detect when a pattern that was +compiled in an environment of one endianness is run in an environment with the +other endianness. This is the error that PCRE gives when the magic number is +not present. +

+  PCRE_ERROR_UNKNOWN_OPCODE (-5)
+

+While running the pattern match, an unknown item was encountered in the +compiled pattern. This error could be caused by a bug in PCRE or by overwriting +of the compiled pattern. +

+  PCRE_ERROR_NOMEMORY       (-6)
+

+If a pattern contains back references, but the ovector that is passed to +pcre_exec() is not big enough to remember the referenced substrings, PCRE +gets a block of memory at the start of matching to use for this purpose. If the +call via pcre_malloc() fails, this error is given. The memory is +automatically freed at the end of matching. +

+This error is also given if pcre_stack_malloc() fails in +pcre_exec(). This can happen only when PCRE has been compiled with +--disable-stack-for-recursion. +

+  PCRE_ERROR_NOSUBSTRING    (-7)
+

+This error is used by the pcre_copy_substring(), +pcre_get_substring(), and pcre_get_substring_list() functions (see +below). It is never returned by pcre_exec(). +

+  PCRE_ERROR_MATCHLIMIT     (-8)
+

+The backtracking limit, as specified by the match_limit field in a +pcre_extra structure (or defaulted) was reached. See the description +above. +

+  PCRE_ERROR_CALLOUT        (-9)
+

+This error is never generated by pcre_exec() itself. It is provided for +use by callout functions that want to yield a distinctive error code. See the +pcrecallout +documentation for details. +

+  PCRE_ERROR_BADUTF8        (-10)
+

+A string that contains an invalid UTF-8 byte sequence was passed as a subject, +and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector +(ovecsize) is at least 2, the byte offset to the start of the the invalid +UTF-8 character is placed in the first element, and a reason code is placed in +the second element. The reason codes are listed in the +following section. +For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a +truncated UTF-8 character at the end of the subject (reason codes 1 to 5), +PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8. +

+  PCRE_ERROR_BADUTF8_OFFSET (-11)
+

+The UTF-8 byte sequence that was passed as a subject was checked and found to +be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of +startoffset did not point to the beginning of a UTF-8 character or the +end of the subject. +

+  PCRE_ERROR_PARTIAL        (-12)
+

+The subject string did not match, but it did match partially. See the +pcrepartial +documentation for details of partial matching. +

+  PCRE_ERROR_BADPARTIAL     (-13)
+

+This code is no longer in use. It was formerly returned when the PCRE_PARTIAL +option was used with a compiled pattern containing items that were not +supported for partial matching. From release 8.00 onwards, there are no +restrictions on partial matching. +

+  PCRE_ERROR_INTERNAL       (-14)
+

+An unexpected internal error has occurred. This error could be caused by a bug +in PCRE or by overwriting of the compiled pattern. +

+  PCRE_ERROR_BADCOUNT       (-15)
+

+This error is given if the value of the ovecsize argument is negative. +

+  PCRE_ERROR_RECURSIONLIMIT (-21)
+

+The internal recursion limit, as specified by the match_limit_recursion +field in a pcre_extra structure (or defaulted) was reached. See the +description above. +

+  PCRE_ERROR_BADNEWLINE     (-23)
+

+An invalid combination of PCRE_NEWLINE_xxx options was given. +

+  PCRE_ERROR_BADOFFSET      (-24)
+

+The value of startoffset was negative or greater than the length of the +subject, that is, the value in length. +

+  PCRE_ERROR_SHORTUTF8      (-25)
+

+This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string +ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set. +Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in +fact sufficient to detect this case, but this special error code for +PCRE_PARTIAL_HARD precedes the implementation of returned information; it is +retained for backwards compatibility. +

+  PCRE_ERROR_RECURSELOOP    (-26)
+

+This error is returned when pcre_exec() detects a recursion loop within +the pattern. Specifically, it means that either the whole pattern or a +subpattern has been called recursively for the second time at the same position +in the subject string. Some simple patterns that might do this are detected and +faulted at compile time, but more complicated cases, in particular mutual +recursions between two different subpatterns, cannot be detected until run +time. +

+  PCRE_ERROR_JIT_STACKLIMIT (-27)
+

+This error is returned when a pattern that was successfully studied using a +JIT compile option is being matched, but the memory available for the +just-in-time processing stack is not large enough. See the +pcrejit +documentation for more details. +

+  PCRE_ERROR_BADMODE        (-28)
+

+This error is given if a pattern that was compiled by the 8-bit library is +passed to a 16-bit or 32-bit library function, or vice versa. +

+  PCRE_ERROR_BADENDIANNESS  (-29)
+

+This error is given if a pattern that was compiled and saved is reloaded on a +host with different endianness. The utility function +pcre_pattern_to_host_byte_order() can be used to convert such a pattern +so that it runs on the new host. +

+  PCRE_ERROR_JIT_BADOPTION
+

+This error is returned when a pattern that was successfully studied using a JIT +compile option is being matched, but the matching mode (partial or complete +match) does not correspond to any JIT compilation mode. When the JIT fast path +function is used, this error may be also given for invalid options. See the +pcrejit +documentation for more details. +

+  PCRE_ERROR_BADLENGTH      (-32)
+

+This error is given if pcre_exec() is called with a negative value for +the length argument. +

+Error numbers -16 to -20, -22, and 30 are not used by pcre_exec(). +

+
+Reason codes for invalid UTF-8 strings +
+

+This section applies only to the 8-bit library. The corresponding information +for the 16-bit and 32-bit libraries is given in the +pcre16 +and +pcre32 +pages. +

+When pcre_exec() returns either PCRE_ERROR_BADUTF8 or +PCRE_ERROR_SHORTUTF8, and the size of the output vector (ovecsize) is at +least 2, the offset of the start of the invalid UTF-8 character is placed in +the first output vector element (ovector[0]) and a reason code is placed +in the second element (ovector[1]). The reason codes are given names in +the pcre.h header file: +

+  PCRE_UTF8_ERR1
+  PCRE_UTF8_ERR2
+  PCRE_UTF8_ERR3
+  PCRE_UTF8_ERR4
+  PCRE_UTF8_ERR5
+

+The string ends with a truncated UTF-8 character; the code specifies how many +bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be +no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279) +allows for up to 6 bytes, and this is checked first; hence the possibility of +4 or 5 missing bytes. +

+  PCRE_UTF8_ERR6
+  PCRE_UTF8_ERR7
+  PCRE_UTF8_ERR8
+  PCRE_UTF8_ERR9
+  PCRE_UTF8_ERR10
+

+The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the +character do not have the binary value 0b10 (that is, either the most +significant bit is 0, or the next bit is 1). +

+  PCRE_UTF8_ERR11
+  PCRE_UTF8_ERR12
+

+A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long; +these code points are excluded by RFC 3629. +

+  PCRE_UTF8_ERR13
+

+A 4-byte character has a value greater than 0x10fff; these code points are +excluded by RFC 3629. +

+  PCRE_UTF8_ERR14
+

+A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of +code points are reserved by RFC 3629 for use with UTF-16, and so are excluded +from UTF-8. +

+  PCRE_UTF8_ERR15
+  PCRE_UTF8_ERR16
+  PCRE_UTF8_ERR17
+  PCRE_UTF8_ERR18
+  PCRE_UTF8_ERR19
+

+A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a +value that can be represented by fewer bytes, which is invalid. For example, +the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just +one byte. +

+  PCRE_UTF8_ERR20
+

+The two most significant bits of the first byte of a character have the binary +value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a +byte can only validly occur as the second or subsequent byte of a multi-byte +character. +

+  PCRE_UTF8_ERR21
+

+The first byte of a character has the value 0xfe or 0xff. These values can +never occur in a valid UTF-8 string. +

+  PCRE_UTF8_ERR22
+

+This error code was formerly used when the presence of a so-called +"non-character" caused an error. Unicode corrigendum #9 makes it clear that +such characters should not cause a string to be rejected, and so this code is +no longer in use and is never returned. +

+
EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
+

+int pcre_copy_substring(const char *subject, int *ovector, + int stringcount, int stringnumber, char *buffer, + int buffersize); +
+
+int pcre_get_substring(const char *subject, int *ovector, + int stringcount, int stringnumber, + const char **stringptr); +
+
+int pcre_get_substring_list(const char *subject, + int *ovector, int stringcount, const char ***listptr); +

+Captured substrings can be accessed directly by using the offsets returned by +pcre_exec() in ovector. For convenience, the functions +pcre_copy_substring(), pcre_get_substring(), and +pcre_get_substring_list() are provided for extracting captured substrings +as new, separate, zero-terminated strings. These functions identify substrings +by number. The next section describes functions for extracting named +substrings. +

+A substring that contains a binary zero is correctly extracted and has a +further zero added on the end, but the result is not, of course, a C string. +However, you can process such a string by referring to the length that is +returned by pcre_copy_substring() and pcre_get_substring(). +Unfortunately, the interface to pcre_get_substring_list() is not adequate +for handling strings containing binary zeros, because the end of the final +string is not independently indicated. +

+The first three arguments are the same for all three of these functions: +subject is the subject string that has just been successfully matched, +ovector is a pointer to the vector of integer offsets that was passed to +pcre_exec(), and stringcount is the number of substrings that were +captured by the match, including the substring that matched the entire regular +expression. This is the value returned by pcre_exec() if it is greater +than zero. If pcre_exec() returned zero, indicating that it ran out of +space in ovector, the value passed as stringcount should be the +number of elements in the vector divided by three. +

+The functions pcre_copy_substring() and pcre_get_substring() +extract a single substring, whose number is given as stringnumber. A +value of zero extracts the substring that matched the entire pattern, whereas +higher values extract the captured substrings. For pcre_copy_substring(), +the string is placed in buffer, whose length is given by +buffersize, while for pcre_get_substring() a new block of memory is +obtained via pcre_malloc, and its address is returned via +stringptr. The yield of the function is the length of the string, not +including the terminating zero, or one of these error codes: +

+  PCRE_ERROR_NOMEMORY       (-6)
+

+The buffer was too small for pcre_copy_substring(), or the attempt to get +memory failed for pcre_get_substring(). +

+  PCRE_ERROR_NOSUBSTRING    (-7)
+

+There is no substring whose number is stringnumber. +

+The pcre_get_substring_list() function extracts all available substrings +and builds a list of pointers to them. All this is done in a single block of +memory that is obtained via pcre_malloc. The address of the memory block +is returned via listptr, which is also the start of the list of string +pointers. The end of the list is marked by a NULL pointer. The yield of the +function is zero if all went well, or the error code +

+  PCRE_ERROR_NOMEMORY       (-6)
+

+if the attempt to get the memory block failed. +

+When any of these functions encounter a substring that is unset, which can +happen when capturing subpattern number n+1 matches some part of the +subject, but subpattern n has not been used at all, they return an empty +string. This can be distinguished from a genuine zero-length substring by +inspecting the appropriate offset in ovector, which is negative for unset +substrings. +

+The two convenience functions pcre_free_substring() and +pcre_free_substring_list() can be used to free the memory returned by +a previous call of pcre_get_substring() or +pcre_get_substring_list(), respectively. They do nothing more than call +the function pointed to by pcre_free, which of course could be called +directly from a C program. However, PCRE is used in some situations where it is +linked via a special interface to another programming language that cannot use +pcre_free directly; it is for these cases that the functions are +provided. +

+
EXTRACTING CAPTURED SUBSTRINGS BY NAME
+

+int pcre_get_stringnumber(const pcre *code, + const char *name); +
+
+int pcre_copy_named_substring(const pcre *code, + const char *subject, int *ovector, + int stringcount, const char *stringname, + char *buffer, int buffersize); +
+
+int pcre_get_named_substring(const pcre *code, + const char *subject, int *ovector, + int stringcount, const char *stringname, + const char **stringptr); +

+To extract a substring by name, you first have to find associated number. +For example, for this pattern +

+  (a+)b(?<xxx>\d+)...
+

+the number of the subpattern called "xxx" is 2. If the name is known to be +unique (PCRE_DUPNAMES was not set), you can find the number from the name by +calling pcre_get_stringnumber(). The first argument is the compiled +pattern, and the second is the name. The yield of the function is the +subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of +that name. +

+Given the number, you can extract the substring directly, or use one of the +functions described in the previous section. For convenience, there are also +two functions that do the whole job. +

+Most of the arguments of pcre_copy_named_substring() and +pcre_get_named_substring() are the same as those for the similarly named +functions that extract by number. As these are described in the previous +section, they are not re-described here. There are just two differences: +

+First, instead of a substring number, a substring name is given. Second, there +is an extra argument, given at the start, which is a pointer to the compiled +pattern. This is needed in order to gain access to the name-to-number +translation table. +

+These functions call pcre_get_stringnumber(), and if it succeeds, they +then call pcre_copy_substring() or pcre_get_substring(), as +appropriate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, +the behaviour may not be what you want (see the next section). +

+Warning: If the pattern uses the (?| feature to set up multiple +subpatterns with the same number, as described in the +section on duplicate subpattern numbers +in the +pcrepattern +page, you cannot use names to distinguish the different subpatterns, because +names are not included in the compiled code. The matching process uses only +numbers. For this reason, the use of different names for subpatterns of the +same number causes an error at compile time. +

+
DUPLICATE SUBPATTERN NAMES
+

+int pcre_get_stringtable_entries(const pcre *code, + const char *name, char **first, char **last); +

+When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns +are not required to be unique. (Duplicate names are always allowed for +subpatterns with the same number, created by using the (?| feature. Indeed, if +such subpatterns are named, they are required to use the same names.) +

+Normally, patterns with duplicate names are such that in any one match, only +one of the named subpatterns participates. An example is shown in the +pcrepattern +documentation. +

+When duplicates are present, pcre_copy_named_substring() and +pcre_get_named_substring() return the first substring corresponding to +the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is +returned; no data is returned. The pcre_get_stringnumber() function +returns one of the numbers that are associated with the name, but it is not +defined which it is. +

+If you want to get full details of all captured substrings for a given name, +you must use the pcre_get_stringtable_entries() function. The first +argument is the compiled pattern, and the second is the name. The third and +fourth are pointers to variables which are updated by the function. After it +has run, they point to the first and last entries in the name-to-number table +for the given name. The function itself returns the length of each entry, or +PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is +described above in the section entitled Information about a pattern +above. +Given all the relevant entries for the name, you can extract each of their +numbers, and hence the captured data, if any. +

+
FINDING ALL POSSIBLE MATCHES
+

+The traditional matching function uses a similar algorithm to Perl, which stops +when it finds the first match, starting at a given point in the subject. If you +want to find all possible matches, or the longest possible match, consider +using the alternative matching function (see below) instead. If you cannot use +the alternative function, but still need to find all possible matches, you +can kludge it up by making use of the callout facility, which is described in +the +pcrecallout +documentation. +

+What you have to do is to insert a callout right at the end of the pattern. +When your callout function is called, extract and save the current matched +substring. Then return 1, which forces pcre_exec() to backtrack and try +other alternatives. Ultimately, when it runs out of matches, pcre_exec() +will yield PCRE_ERROR_NOMATCH. +

+
OBTAINING AN ESTIMATE OF STACK USAGE
+

+Matching certain patterns using pcre_exec() can use a lot of process +stack, which in certain environments can be rather limited in size. Some users +find it helpful to have an estimate of the amount of stack that is used by +pcre_exec(), to help them set recursion limits, as described in the +pcrestack +documentation. The estimate that is output by pcretest when called with +the -m and -C options is obtained by calling pcre_exec with +the values NULL, NULL, NULL, -999, and -999 for its first five arguments. +

+Normally, if its first argument is NULL, pcre_exec() immediately returns +the negative error code PCRE_ERROR_NULL, but with this special combination of +arguments, it returns instead a negative number whose absolute value is the +approximate stack frame size in bytes. (A negative number is used so that it is +clear that no match has happened.) The value is approximate because in some +cases, recursive calls to pcre_exec() occur when there are one or two +additional variables on the stack. +

+If PCRE has been compiled to use the heap instead of the stack for recursion, +the value returned is the size of each block that is obtained from the heap. +

+
MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
+

+int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, + const char *subject, int length, int startoffset, + int options, int *ovector, int ovecsize, + int *workspace, int wscount); +

+The function pcre_dfa_exec() is called to match a subject string against +a compiled pattern, using a matching algorithm that scans the subject string +just once, and does not backtrack. This has different characteristics to the +normal algorithm, and is not compatible with Perl. Some of the features of PCRE +patterns are not supported. Nevertheless, there are times when this kind of +matching can be useful. For a discussion of the two matching algorithms, and a +list of features that pcre_dfa_exec() does not support, see the +pcrematching +documentation. +

+The arguments for the pcre_dfa_exec() function are the same as for +pcre_exec(), plus two extras. The ovector argument is used in a +different way, and this is described below. The other common arguments are used +in the same way as for pcre_exec(), so their description is not repeated +here. +

+The two additional arguments provide workspace for the function. The workspace +vector should contain at least 20 elements. It is used for keeping track of +multiple paths through the pattern tree. More workspace will be needed for +patterns and subjects where there are a lot of potential matches. +

+Here is an example of a simple call to pcre_dfa_exec(): +

+  int rc;
+  int ovector[10];
+  int wspace[20];
+  rc = pcre_dfa_exec(
+    re,             /* result of pcre_compile() */
+    NULL,           /* we didn't study the pattern */
+    "some string",  /* the subject string */
+    11,             /* the length of the subject string */
+    0,              /* start at offset 0 in the subject */
+    0,              /* default options */
+    ovector,        /* vector of integers for substring information */
+    10,             /* number of elements (NOT size in bytes) */
+    wspace,         /* working space vector */
+    20);            /* number of elements (NOT size in bytes) */
+

+
+Option bits for pcre_dfa_exec() +
+

+The unused bits of the options argument for pcre_dfa_exec() must be +zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx, +PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, +PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, +PCRE_PARTIAL_HARD, PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. +All but the last four of these are exactly the same as for pcre_exec(), +so their description is not repeated here. +

+  PCRE_PARTIAL_HARD
+  PCRE_PARTIAL_SOFT
+

+These have the same general effect as they do for pcre_exec(), but the +details are slightly different. When PCRE_PARTIAL_HARD is set for +pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the subject +is reached and there is still at least one matching possibility that requires +additional characters. This happens even if some complete matches have also +been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH +is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached, +there have been no complete matches, but there is still at least one matching +possibility. The portion of the string that was inspected when the longest +partial match was found is set as the first matching string in both cases. +There is a more detailed discussion of partial and multi-segment matching, with +examples, in the +pcrepartial +documentation. +

+  PCRE_DFA_SHORTEST
+

+Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as +soon as it has found one match. Because of the way the alternative algorithm +works, this is necessarily the shortest possible match at the first possible +matching point in the subject string. +

+  PCRE_DFA_RESTART
+

+When pcre_dfa_exec() returns a partial match, it is possible to call it +again, with additional subject characters, and have it continue with the same +match. The PCRE_DFA_RESTART option requests this action; when it is set, the +workspace and wscount options must reference the same vector as +before because data about the match so far is left in them after a partial +match. There is more discussion of this facility in the +pcrepartial +documentation. +

+
+Successful returns from pcre_dfa_exec() +
+

+When pcre_dfa_exec() succeeds, it may have matched more than one +substring in the subject. Note, however, that all the matches from one run of +the function start at the same point in the subject. The shorter matches are +all initial substrings of the longer matches. For example, if the pattern +

+  <.*>
+

+is matched against the string +

+  This is <something> <something else> <something further> no more
+

+the three matched strings are +

+  <something>
+  <something> <something else>
+  <something> <something else> <something further>
+

+On success, the yield of the function is a number greater than zero, which is +the number of matched substrings. The substrings themselves are returned in +ovector. Each string uses two elements; the first is the offset to the +start, and the second is the offset to the end. In fact, all the strings have +the same start offset. (Space could have been saved by giving this only once, +but it was decided to retain some compatibility with the way pcre_exec() +returns data, even though the meaning of the strings is different.) +

+The strings are returned in reverse order of length; that is, the longest +matching string is given first. If there were too many matches to fit into +ovector, the yield of the function is zero, and the vector is filled with +the longest matches. Unlike pcre_exec(), pcre_dfa_exec() can use +the entire ovector for returning matched strings. +

+NOTE: PCRE's "auto-possessification" optimization usually applies to character +repeats at the end of a pattern (as well as internally). For example, the +pattern "a\d+" is compiled as if it were "a\d++" because there is no point +even considering the possibility of backtracking into the repeated digits. For +DFA matching, this means that only one possible match is found. If you really +do want multiple matches in such cases, either use an ungreedy repeat +("a\d+?") or set the PCRE_NO_AUTO_POSSESS option when compiling. +

+
+Error returns from pcre_dfa_exec() +
+

+The pcre_dfa_exec() function returns a negative number when it fails. +Many of the errors are the same as for pcre_exec(), and these are +described +above. +There are in addition the following errors that are specific to +pcre_dfa_exec(): +

+  PCRE_ERROR_DFA_UITEM      (-16)
+

+This return is given if pcre_dfa_exec() encounters an item in the pattern +that it does not support, for instance, the use of \C or a back reference. +

+  PCRE_ERROR_DFA_UCOND      (-17)
+

+This return is given if pcre_dfa_exec() encounters a condition item that +uses a back reference for the condition, or a test for recursion in a specific +group. These are not supported. +

+  PCRE_ERROR_DFA_UMLIMIT    (-18)
+

+This return is given if pcre_dfa_exec() is called with an extra +block that contains a setting of the match_limit or +match_limit_recursion fields. This is not supported (these fields are +meaningless for DFA matching). +

+  PCRE_ERROR_DFA_WSSIZE     (-19)
+

+This return is given if pcre_dfa_exec() runs out of space in the +workspace vector. +

+  PCRE_ERROR_DFA_RECURSE    (-20)
+

+When a recursive subpattern is processed, the matching function calls itself +recursively, using private vectors for ovector and workspace. This +error is given if the output vector is not large enough. This should be +extremely rare, as a vector of size 1000 is used. +

+  PCRE_ERROR_DFA_BADRESTART (-30)
+

+When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, +some plausibility checks are made on the contents of the workspace, which +should contain data about the previous partial match. If any of these checks +fail, this error is given. +

+
SEE ALSO
+

+pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), +pcrecpp(3)(3), pcrematching(3), pcrepartial(3), +pcreposix(3), pcreprecompile(3), pcresample(3), +pcrestack(3). +

+
AUTHOR
+

+Philip Hazel +
+University Computing Service +
+Cambridge CB2 3QH, England. +
+

+
REVISION
+

+Return to the PCRE index page. +

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