--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/libraries/spcre/libpcre/pcre/doc/pcreapi.3 Wed Jun 23 15:52:26 2010 +0100
@@ -0,0 +1,1983 @@
+.TH PCREAPI 3
+.SH NAME
+PCRE - Perl-compatible regular expressions
+.SH "PCRE NATIVE API"
+.rs
+.sp
+.B #include <pcre.h>
+.PP
+.SM
+.B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
+.ti +5n
+.B const char **\fIerrptr\fP, int *\fIerroffset\fP,
+.ti +5n
+.B const unsigned char *\fItableptr\fP);
+.PP
+.B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
+.ti +5n
+.B int *\fIerrorcodeptr\fP,
+.ti +5n
+.B const char **\fIerrptr\fP, int *\fIerroffset\fP,
+.ti +5n
+.B const unsigned char *\fItableptr\fP);
+.PP
+.B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
+.ti +5n
+.B const char **\fIerrptr\fP);
+.PP
+.B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
+.ti +5n
+.B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
+.ti +5n
+.B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
+.PP
+.B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
+.ti +5n
+.B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
+.ti +5n
+.B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
+.ti +5n
+.B int *\fIworkspace\fP, int \fIwscount\fP);
+.PP
+.B int pcre_copy_named_substring(const pcre *\fIcode\fP,
+.ti +5n
+.B const char *\fIsubject\fP, int *\fIovector\fP,
+.ti +5n
+.B int \fIstringcount\fP, const char *\fIstringname\fP,
+.ti +5n
+.B char *\fIbuffer\fP, int \fIbuffersize\fP);
+.PP
+.B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
+.ti +5n
+.B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
+.ti +5n
+.B int \fIbuffersize\fP);
+.PP
+.B int pcre_get_named_substring(const pcre *\fIcode\fP,
+.ti +5n
+.B const char *\fIsubject\fP, int *\fIovector\fP,
+.ti +5n
+.B int \fIstringcount\fP, const char *\fIstringname\fP,
+.ti +5n
+.B const char **\fIstringptr\fP);
+.PP
+.B int pcre_get_stringnumber(const pcre *\fIcode\fP,
+.ti +5n
+.B const char *\fIname\fP);
+.PP
+.B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
+.ti +5n
+.B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
+.PP
+.B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
+.ti +5n
+.B int \fIstringcount\fP, int \fIstringnumber\fP,
+.ti +5n
+.B const char **\fIstringptr\fP);
+.PP
+.B int pcre_get_substring_list(const char *\fIsubject\fP,
+.ti +5n
+.B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
+.PP
+.B void pcre_free_substring(const char *\fIstringptr\fP);
+.PP
+.B void pcre_free_substring_list(const char **\fIstringptr\fP);
+.PP
+.B const unsigned char *pcre_maketables(void);
+.PP
+.B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
+.ti +5n
+.B int \fIwhat\fP, void *\fIwhere\fP);
+.PP
+.B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
+.B *\fIfirstcharptr\fP);
+.PP
+.B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
+.PP
+.B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
+.PP
+.B char *pcre_version(void);
+.PP
+.B void *(*pcre_malloc)(size_t);
+.PP
+.B void (*pcre_free)(void *);
+.PP
+.B void *(*pcre_stack_malloc)(size_t);
+.PP
+.B void (*pcre_stack_free)(void *);
+.PP
+.B int (*pcre_callout)(pcre_callout_block *);
+.
+.
+.SH "PCRE API OVERVIEW"
+.rs
+.sp
+PCRE has its own native API, which is described in this document. There are
+also some wrapper functions that correspond to the POSIX regular expression
+API. These are described in the
+.\" HREF
+\fBpcreposix\fP
+.\"
+documentation. Both of these APIs define a set of C function calls. A C++
+wrapper is distributed with PCRE. It is documented in the
+.\" HREF
+\fBpcrecpp\fP
+.\"
+page.
+.P
+The native API C function prototypes are defined in the header file
+\fBpcre.h\fP, and on Unix systems the library itself is called \fBlibpcre\fP.
+It can normally be accessed by adding \fB-lpcre\fP 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.
+.P
+The functions \fBpcre_compile()\fP, \fBpcre_compile2()\fP, \fBpcre_study()\fP,
+and \fBpcre_exec()\fP 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 \fIpcredemo.c\fP in the source
+distribution. The
+.\" HREF
+\fBpcresample\fP
+.\"
+documentation describes how to compile and run it.
+.P
+A second matching function, \fBpcre_dfa_exec()\fP, 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. However, this algorithm
+does not return captured substrings. A description of the two matching
+algorithms and their advantages and disadvantages is given in the
+.\" HREF
+\fBpcrematching\fP
+.\"
+documentation.
+.P
+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 \fBpcre_exec()\fP. They are:
+.sp
+ \fBpcre_copy_substring()\fP
+ \fBpcre_copy_named_substring()\fP
+ \fBpcre_get_substring()\fP
+ \fBpcre_get_named_substring()\fP
+ \fBpcre_get_substring_list()\fP
+ \fBpcre_get_stringnumber()\fP
+ \fBpcre_get_stringtable_entries()\fP
+.sp
+\fBpcre_free_substring()\fP and \fBpcre_free_substring_list()\fP are also
+provided, to free the memory used for extracted strings.
+.P
+The function \fBpcre_maketables()\fP is used to build a set of character tables
+in the current locale for passing to \fBpcre_compile()\fP, \fBpcre_exec()\fP,
+or \fBpcre_dfa_exec()\fP. 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.
+.P
+The function \fBpcre_fullinfo()\fP is used to find out information about a
+compiled pattern; \fBpcre_info()\fP is an obsolete version that returns only
+some of the available information, but is retained for backwards compatibility.
+The function \fBpcre_version()\fP returns a pointer to a string containing the
+version of PCRE and its date of release.
+.P
+The function \fBpcre_refcount()\fP maintains a reference count in a data block
+containing a compiled pattern. This is provided for the benefit of
+object-oriented applications.
+.P
+The global variables \fBpcre_malloc\fP and \fBpcre_free\fP initially contain
+the entry points of the standard \fBmalloc()\fP and \fBfree()\fP 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.
+.P
+The global variables \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP 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 \fBpcre_exec()\fP function. See the
+.\" HREF
+\fBpcrebuild\fP
+.\"
+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
+.\" HREF
+\fBpcrestack\fP
+.\"
+documentation.
+.P
+The global variable \fBpcre_callout\fP 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
+.\" HREF
+\fBpcrecallout\fP
+.\"
+documentation.
+.
+.
+.\" HTML <a name="newlines"></a>
+.SH NEWLINES
+.rs
+.sp
+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 (formfeed,
+U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
+(paragraph separator, U+2029).
+.P
+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.
+.P
+At compile time, the newline convention can be specified by the \fIoptions\fP
+argument of \fBpcre_compile()\fP, or it can be specified by special text at the
+start of the pattern itself; this overrides any other settings. See the
+.\" HREF
+\fBpcrepattern\fP
+.\"
+page for details of the special character sequences.
+.P
+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
+.\" HTML <a href="#execoptions">
+.\" </a>
+section on \fBpcre_exec()\fP options
+.\"
+below.
+.P
+The choice of newline convention does not affect the interpretation of
+the \en or \er escape sequences, nor does it affect what \eR matches, which is
+controlled in a similar way, but by separate options.
+.
+.
+.SH MULTITHREADING
+.rs
+.sp
+The PCRE functions can be used in multi-threading applications, with the
+proviso that the memory management functions pointed to by \fBpcre_malloc\fP,
+\fBpcre_free\fP, \fBpcre_stack_malloc\fP, and \fBpcre_stack_free\fP, and the
+callout function pointed to by \fBpcre_callout\fP, are shared by all threads.
+.P
+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.
+.
+.
+.SH "SAVING PRECOMPILED PATTERNS FOR LATER USE"
+.rs
+.sp
+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
+.\" HREF
+\fBpcreprecompile\fP
+.\"
+documentation. 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.
+.
+.
+.SH "CHECKING BUILD-TIME OPTIONS"
+.rs
+.sp
+.B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
+.PP
+The function \fBpcre_config()\fP makes it possible for a PCRE client to
+discover which optional features have been compiled into the PCRE library. The
+.\" HREF
+\fBpcrebuild\fP
+.\"
+documentation has more details about these optional features.
+.P
+The first argument for \fBpcre_config()\fP is an integer, specifying which
+information is required; the second argument is a pointer to a variable into
+which the information is placed. The following information is available:
+.sp
+ PCRE_CONFIG_UTF8
+.sp
+The output is an integer that is set to one if UTF-8 support is available;
+otherwise it is set to zero.
+.sp
+ PCRE_CONFIG_UNICODE_PROPERTIES
+.sp
+The output is an integer that is set to one if support for Unicode character
+properties is available; otherwise it is set to zero.
+.sp
+ PCRE_CONFIG_NEWLINE
+.sp
+The output is an integer whose value specifies the default character sequence
+that is recognized as meaning "newline". The four values that are supported
+are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. The
+default should normally be the standard sequence for your operating system.
+.sp
+ PCRE_CONFIG_BSR
+.sp
+The output is an integer whose value indicates what character sequences the \eR
+escape sequence matches by default. A value of 0 means that \eR matches any
+Unicode line ending sequence; a value of 1 means that \eR matches only CR, LF,
+or CRLF. The default can be overridden when a pattern is compiled or matched.
+.sp
+ PCRE_CONFIG_LINK_SIZE
+.sp
+The output is an integer that contains the number of bytes used for internal
+linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
+allow larger regular expressions to be compiled, at the expense of slower
+matching. 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.
+.sp
+ PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
+.sp
+The output is an integer that contains the threshold above which the POSIX
+interface uses \fBmalloc()\fP for output vectors. Further details are given in
+the
+.\" HREF
+\fBpcreposix\fP
+.\"
+documentation.
+.sp
+ PCRE_CONFIG_MATCH_LIMIT
+.sp
+The output is an integer that gives the default limit for the number of
+internal matching function calls in a \fBpcre_exec()\fP execution. Further
+details are given with \fBpcre_exec()\fP below.
+.sp
+ PCRE_CONFIG_MATCH_LIMIT_RECURSION
+.sp
+The output is an integer that gives the default limit for the depth of
+recursion when calling the internal matching function in a \fBpcre_exec()\fP
+execution. Further details are given with \fBpcre_exec()\fP below.
+.sp
+ PCRE_CONFIG_STACKRECURSE
+.sp
+The output is an integer that is set to one if internal recursion when running
+\fBpcre_exec()\fP 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, \fBpcre_stack_malloc\fP and
+\fBpcre_stack_free\fP are called to manage memory blocks on the heap, thus
+avoiding the use of the stack.
+.
+.
+.SH "COMPILING A PATTERN"
+.rs
+.sp
+.B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
+.ti +5n
+.B const char **\fIerrptr\fP, int *\fIerroffset\fP,
+.ti +5n
+.B const unsigned char *\fItableptr\fP);
+.sp
+.B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
+.ti +5n
+.B int *\fIerrorcodeptr\fP,
+.ti +5n
+.B const char **\fIerrptr\fP, int *\fIerroffset\fP,
+.ti +5n
+.B const unsigned char *\fItableptr\fP);
+.P
+Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be
+called to compile a pattern into an internal form. The only difference between
+the two interfaces is that \fBpcre_compile2()\fP has an additional argument,
+\fIerrorcodeptr\fP, via which a numerical error code can be returned.
+.P
+The pattern is a C string terminated by a binary zero, and is passed in the
+\fIpattern\fP argument. A pointer to a single block of memory that is obtained
+via \fBpcre_malloc\fP is returned. This contains the compiled code and related
+data. The \fBpcre\fP 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 \fBpcre_free\fP) when it is no longer required.
+.P
+Although the compiled code of a PCRE regex is relocatable, that is, it does not
+depend on memory location, the complete \fBpcre\fP data block is not
+fully relocatable, because it may contain a copy of the \fItableptr\fP
+argument, which is an address (see below).
+.P
+The \fIoptions\fP 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, can also be set and unset from within the pattern (see
+the detailed description in the
+.\" HREF
+\fBpcrepattern\fP
+.\"
+documentation). For these options, the contents of the \fIoptions\fP argument
+specifies their initial settings at the start of compilation and execution. The
+PCRE_ANCHORED and PCRE_NEWLINE_\fIxxx\fP options can be set at the time of
+matching as well as at compile time.
+.P
+If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
+Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
+NULL, and sets the variable pointed to by \fIerrptr\fP 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. The offset from the start of the pattern to the character
+where the error was discovered is placed in the variable pointed to by
+\fIerroffset\fP, which must not be NULL. If it is, an immediate error is given.
+.P
+If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the
+\fIerrorcodeptr\fP 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.
+.P
+If the final argument, \fItableptr\fP, is NULL, PCRE uses a default set of
+character tables that are built when PCRE is compiled, using the default C
+locale. Otherwise, \fItableptr\fP must be an address that is the result of a
+call to \fBpcre_maketables()\fP. This value is stored with the compiled
+pattern, and used again by \fBpcre_exec()\fP, unless another table pointer is
+passed to it. For more discussion, see the section on locale support below.
+.P
+This code fragment shows a typical straightforward call to \fBpcre_compile()\fP:
+.sp
+ 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 */
+.sp
+The following names for option bits are defined in the \fBpcre.h\fP header
+file:
+.sp
+ PCRE_ANCHORED
+.sp
+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.
+.sp
+ PCRE_AUTO_CALLOUT
+.sp
+If this bit is set, \fBpcre_compile()\fP automatically inserts callout items,
+all with number 255, before each pattern item. For discussion of the callout
+facility, see the
+.\" HREF
+\fBpcrecallout\fP
+.\"
+documentation.
+.sp
+ PCRE_BSR_ANYCRLF
+ PCRE_BSR_UNICODE
+.sp
+These options (which are mutually exclusive) control what the \eR 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.
+.sp
+ PCRE_CASELESS
+.sp
+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.
+.sp
+ PCRE_DOLLAR_ENDONLY
+.sp
+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.
+.sp
+ PCRE_DOTALL
+.sp
+If this bit is set, a dot metacharater in the pattern matches all characters,
+including those that indicate newline. Without it, 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.
+.sp
+ PCRE_DUPNAMES
+.sp
+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
+.\" HREF
+\fBpcrepattern\fP
+.\"
+documentation.
+.sp
+ PCRE_EXTENDED
+.sp
+If this bit is set, whitespace data characters in the pattern are totally
+ignored except when escaped or inside a character class. Whitespace does not
+include the VT character (code 11). In addition, characters between an
+unescaped # outside a character class and the next newline, inclusive, are also
+ignored. This is equivalent to Perl's /x option, and it can be changed within a
+pattern by a (?x) option setting.
+.P
+This option makes it possible to include comments inside complicated patterns.
+Note, however, that this applies only to data characters. Whitespace characters
+may never appear within special character sequences in a pattern, for example
+within the sequence (?( which introduces a conditional subpattern.
+.sp
+ PCRE_EXTRA
+.sp
+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 a warning for this.) There are at present no other features controlled by
+this option. It can also be set by a (?X) option setting within a pattern.
+.sp
+ PCRE_FIRSTLINE
+.sp
+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.
+.sp
+ PCRE_JAVASCRIPT_COMPAT
+.sp
+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:
+.P
+(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.
+.P
+(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 (\e1)(a) succeeds when this option is set (assuming it can find
+an "a" in the subject), whereas it fails by default, for Perl compatibility.
+.sp
+ PCRE_MULTILINE
+.sp
+By default, 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, while the "end of
+line" metacharacter ($) matches only at the end of the string, or before a
+terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
+Perl.
+.P
+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.
+.sp
+ PCRE_NEWLINE_CR
+ PCRE_NEWLINE_LF
+ PCRE_NEWLINE_CRLF
+ PCRE_NEWLINE_ANYCRLF
+ PCRE_NEWLINE_ANY
+.sp
+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. The Unicode newline
+sequences are the three just mentioned, plus the single characters VT (vertical
+tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
+separator, U+2028), and PS (paragraph separator, U+2029). The last two are
+recognized only in UTF-8 mode.
+.P
+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.
+.P
+The only time that a line break is specially recognized when compiling a
+pattern is if PCRE_EXTENDED is set, and an unescaped # outside a character
+class is encountered. This indicates a comment that lasts until after the next
+line break sequence. In other circumstances, line break sequences are treated
+as literal data, except that in PCRE_EXTENDED mode, both CR and LF are treated
+as whitespace characters and are therefore ignored.
+.P
+The newline option that is set at compile time becomes the default that is used
+for \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, but it can be overridden.
+.sp
+ PCRE_NO_AUTO_CAPTURE
+.sp
+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.
+.sp
+ PCRE_UNGREEDY
+.sp
+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.
+.sp
+ PCRE_UTF8
+.sp
+This option causes PCRE to regard both the pattern and the subject as strings
+of UTF-8 characters instead of single-byte character strings. However, it is
+available only when PCRE is built to include UTF-8 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
+.\" HTML <a href="pcre.html#utf8support">
+.\" </a>
+section on UTF-8 support
+.\"
+in the main
+.\" HREF
+\fBpcre\fP
+.\"
+page.
+.sp
+ PCRE_NO_UTF8_CHECK
+.sp
+When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
+automatically checked. There is a discussion about the
+.\" HTML <a href="pcre.html#utf8strings">
+.\" </a>
+validity of UTF-8 strings
+.\"
+in the main
+.\" HREF
+\fBpcre\fP
+.\"
+page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_compile()\fP
+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. Note that this option
+can also be passed to \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, to suppress
+the UTF-8 validity checking of subject strings.
+.
+.
+.SH "COMPILATION ERROR CODES"
+.rs
+.sp
+The following table lists the error codes than may be returned by
+\fBpcre_compile2()\fP, along with the error messages that may be returned by
+both compiling functions. As PCRE has developed, some error codes have fallen
+out of use. To avoid confusion, they have not been re-used.
+.sp
+ 0 no error
+ 1 \e at end of pattern
+ 2 \ec at end of pattern
+ 3 unrecognized character follows \e
+ 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 not compiled with PCRE_UTF8 support
+ 33 [this code is not in use]
+ 34 character value in \ex{...} sequence is too large
+ 35 invalid condition (?(0)
+ 36 \eC not allowed in lookbehind assertion
+ 37 PCRE does not support \eL, \el, \eN, \eU, or \eu
+ 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
+ 45 support for \eP, \ep, and \eX has not been compiled
+ 46 malformed \eP or \ep sequence
+ 47 unknown property name after \eP or \ep
+ 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 \e377 (not in 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 \eg 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 (*VERB) with an argument is not supported
+ 60 (*VERB) not recognized
+ 61 number is too big
+ 62 subpattern name expected
+ 63 digit expected after (?+
+ 64 ] is an invalid data character in JavaScript compatibility mode
+.sp
+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.
+.
+.
+.SH "STUDYING A PATTERN"
+.rs
+.sp
+.B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP
+.ti +5n
+.B const char **\fIerrptr\fP);
+.PP
+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 \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
+argument. If studying the pattern produces additional information that will
+help speed up matching, \fBpcre_study()\fP returns a pointer to a
+\fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
+results of the study.
+.P
+The returned value from \fBpcre_study()\fP can be passed directly to
+\fBpcre_exec()\fP. However, a \fBpcre_extra\fP block also contains other
+fields that can be set by the caller before the block is passed; these are
+described
+.\" HTML <a href="#extradata">
+.\" </a>
+below
+.\"
+in the section on matching a pattern.
+.P
+If studying the pattern does not produce any additional information
+\fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
+wants to pass any of the other fields to \fBpcre_exec()\fP, it must set up its
+own \fBpcre_extra\fP block.
+.P
+The second argument of \fBpcre_study()\fP contains option bits. At present, no
+options are defined, and this argument should always be zero.
+.P
+The third argument for \fBpcre_study()\fP 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 \fBpcre_study()\fP, to be
+sure that it has run successfully.
+.P
+This is a typical call to \fBpcre_study\fP():
+.sp
+ pcre_extra *pe;
+ pe = pcre_study(
+ re, /* result of pcre_compile() */
+ 0, /* no options exist */
+ &error); /* set to NULL or points to a message */
+.sp
+At present, studying a pattern is useful only for non-anchored patterns that do
+not have a single fixed starting character. A bitmap of possible starting
+bytes is created.
+.
+.
+.\" HTML <a name="localesupport"></a>
+.SH "LOCALE SUPPORT"
+.rs
+.sp
+PCRE handles caseless matching, and determines whether characters are letters,
+digits, or whatever, by reference to a set of tables, indexed by character
+value. When running in UTF-8 mode, this applies only to characters with codes
+less than 128. Higher-valued codes never match escapes such as \ew or \ed, but
+can be tested with \ep if PCRE is built with Unicode character property
+support. The use of locales with Unicode is discouraged. If you are handling
+characters with codes greater than 128, you should either use UTF-8 and
+Unicode, or use locales, but not try to mix the two.
+.P
+PCRE contains an internal set of tables that are used when the final argument
+of \fBpcre_compile()\fP 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.
+.P
+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.
+.P
+External tables are built by calling the \fBpcre_maketables()\fP function,
+which has no arguments, in the relevant locale. The result can then be passed
+to \fBpcre_compile()\fP or \fBpcre_exec()\fP 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:
+.sp
+ setlocale(LC_CTYPE, "fr_FR");
+ tables = pcre_maketables();
+ re = pcre_compile(..., tables);
+.sp
+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".
+.P
+When \fBpcre_maketables()\fP runs, the tables are built in memory that is
+obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
+that the memory containing the tables remains available for as long as it is
+needed.
+.P
+The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
+pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
+and normally also by \fBpcre_exec()\fP. Thus, by default, for any single
+pattern, compilation, studying and matching all happen in the same locale, but
+different patterns can be compiled in different locales.
+.P
+It is possible to pass a table pointer or NULL (indicating the use of the
+internal tables) to \fBpcre_exec()\fP. Although not intended for this purpose,
+this facility could be used to match a pattern in a different locale from the
+one in which it was compiled. Passing table pointers at run time is discussed
+below in the section on matching a pattern.
+.
+.
+.SH "INFORMATION ABOUT A PATTERN"
+.rs
+.sp
+.B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
+.ti +5n
+.B int \fIwhat\fP, void *\fIwhere\fP);
+.PP
+The \fBpcre_fullinfo()\fP function returns information about a compiled
+pattern. It replaces the obsolete \fBpcre_info()\fP function, which is
+nevertheless retained for backwards compability (and is documented below).
+.P
+The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
+pattern. The second argument is the result of \fBpcre_study()\fP, 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:
+.sp
+ PCRE_ERROR_NULL the argument \fIcode\fP was NULL
+ the argument \fIwhere\fP was NULL
+ PCRE_ERROR_BADMAGIC the "magic number" was not found
+ PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
+.sp
+The "magic number" is placed at the start of each compiled pattern as an simple
+check against passing an arbitrary memory pointer. Here is a typical call of
+\fBpcre_fullinfo()\fP, to obtain the length of the compiled pattern:
+.sp
+ int rc;
+ size_t length;
+ rc = pcre_fullinfo(
+ re, /* result of pcre_compile() */
+ pe, /* result of pcre_study(), or NULL */
+ PCRE_INFO_SIZE, /* what is required */
+ &length); /* where to put the data */
+.sp
+The possible values for the third argument are defined in \fBpcre.h\fP, and are
+as follows:
+.sp
+ PCRE_INFO_BACKREFMAX
+.sp
+Return the number of the highest back reference in the pattern. The fourth
+argument should point to an \fBint\fP variable. Zero is returned if there are
+no back references.
+.sp
+ PCRE_INFO_CAPTURECOUNT
+.sp
+Return the number of capturing subpatterns in the pattern. The fourth argument
+should point to an \fBint\fP variable.
+.sp
+ PCRE_INFO_DEFAULT_TABLES
+.sp
+Return a pointer to the internal default character tables within PCRE. The
+fourth argument should point to an \fBunsigned char *\fP variable. This
+information call is provided for internal use by the \fBpcre_study()\fP
+function. External callers can cause PCRE to use its internal tables by passing
+a NULL table pointer.
+.sp
+ PCRE_INFO_FIRSTBYTE
+.sp
+Return information about the first byte of any matched string, for a
+non-anchored pattern. The fourth argument should point to an \fBint\fP
+variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
+still recognized for backwards compatibility.)
+.P
+If there is a fixed first byte, for example, from a pattern such as
+(cat|cow|coyote), its value is returned. Otherwise, if either
+.sp
+(a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
+starts with "^", or
+.sp
+(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
+(if it were set, the pattern would be anchored),
+.sp
+-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.
+.sp
+ PCRE_INFO_FIRSTTABLE
+.sp
+If the pattern was studied, and this resulted in the construction of a 256-bit
+table indicating a fixed set of bytes for the first byte in any matching
+string, a pointer to the table is returned. Otherwise NULL is returned. The
+fourth argument should point to an \fBunsigned char *\fP variable.
+.sp
+ PCRE_INFO_HASCRORLF
+.sp
+Return 1 if the pattern contains any explicit matches for CR or LF characters,
+otherwise 0. The fourth argument should point to an \fBint\fP variable. An
+explicit match is either a literal CR or LF character, or \er or \en.
+.sp
+ PCRE_INFO_JCHANGED
+.sp
+Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
+0. The fourth argument should point to an \fBint\fP variable. (?J) and
+(?-J) set and unset the local PCRE_DUPNAMES option, respectively.
+.sp
+ PCRE_INFO_LASTLITERAL
+.sp
+Return the value of the rightmost literal byte that must exist in any matched
+string, other than at its start, if such a byte has been recorded. The fourth
+argument should point to an \fBint\fP variable. If there is no such byte, -1 is
+returned. For anchored patterns, a last literal byte is recorded only if it
+follows something of variable length. For example, for the pattern
+/^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
+is -1.
+.sp
+ PCRE_INFO_NAMECOUNT
+ PCRE_INFO_NAMEENTRYSIZE
+ PCRE_INFO_NAMETABLE
+.sp
+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
+\fBpcre_get_named_substring()\fP 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 \fBpcre_exec()\fP below). To do the conversion,
+you need to use the name-to-number map, which is described by these three
+values.
+.P
+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 \fBint\fP 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 (a pointer to \fBchar\fP). The first two bytes of each entry
+are the number of the capturing parenthesis, most significant byte first. The
+rest of the entry is the corresponding name, zero terminated. The names are in
+alphabetical order. When PCRE_DUPNAMES is set, duplicate names are in order of
+their parentheses numbers. For example, consider the following pattern (assume
+PCRE_EXTENDED is set, so white space - including newlines - is ignored):
+.sp
+.\" JOIN
+ (?<date> (?<year>(\ed\ed)?\ed\ed) -
+ (?<month>\ed\ed) - (?<day>\ed\ed) )
+.sp
+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 ??:
+.sp
+ 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 ??
+.sp
+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.
+.sp
+ PCRE_INFO_OKPARTIAL
+.sp
+Return 1 if the pattern can be used for partial matching, otherwise 0. The
+fourth argument should point to an \fBint\fP variable. The
+.\" HREF
+\fBpcrepartial\fP
+.\"
+documentation lists the restrictions that apply to patterns when partial
+matching is used.
+.sp
+ PCRE_INFO_OPTIONS
+.sp
+Return a copy of the options with which the pattern was compiled. The fourth
+argument should point to an \fBunsigned long int\fP variable. These option bits
+are those specified in the call to \fBpcre_compile()\fP, 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.
+.P
+A pattern is automatically anchored by PCRE if all of its top-level
+alternatives begin with one of the following:
+.sp
+ ^ unless PCRE_MULTILINE is set
+ \eA always
+ \eG always
+.\" JOIN
+ .* if PCRE_DOTALL is set and there are no back
+ references to the subpattern in which .* appears
+.sp
+For such patterns, the PCRE_ANCHORED bit is set in the options returned by
+\fBpcre_fullinfo()\fP.
+.sp
+ PCRE_INFO_SIZE
+.sp
+Return the size of the compiled pattern, that is, the value that was passed as
+the argument to \fBpcre_malloc()\fP when PCRE was getting memory in which to
+place the compiled data. The fourth argument should point to a \fBsize_t\fP
+variable.
+.sp
+ PCRE_INFO_STUDYSIZE
+.sp
+Return the size of the data block pointed to by the \fIstudy_data\fP field in
+a \fBpcre_extra\fP block. That is, it is the value that was passed to
+\fBpcre_malloc()\fP when PCRE was getting memory into which to place the data
+created by \fBpcre_study()\fP. The fourth argument should point to a
+\fBsize_t\fP variable.
+.
+.
+.SH "OBSOLETE INFO FUNCTION"
+.rs
+.sp
+.B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
+.B *\fIfirstcharptr\fP);
+.PP
+The \fBpcre_info()\fP function is now obsolete because its interface is too
+restrictive to return all the available data about a compiled pattern. New
+programs should use \fBpcre_fullinfo()\fP instead. The yield of
+\fBpcre_info()\fP is the number of capturing subpatterns, or one of the
+following negative numbers:
+.sp
+ PCRE_ERROR_NULL the argument \fIcode\fP was NULL
+ PCRE_ERROR_BADMAGIC the "magic number" was not found
+.sp
+If the \fIoptptr\fP argument is not NULL, a copy of the options with which the
+pattern was compiled is placed in the integer it points to (see
+PCRE_INFO_OPTIONS above).
+.P
+If the pattern is not anchored and the \fIfirstcharptr\fP argument is not NULL,
+it is used to pass back information about the first character of any matched
+string (see PCRE_INFO_FIRSTBYTE above).
+.
+.
+.SH "REFERENCE COUNTS"
+.rs
+.sp
+.B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
+.PP
+The \fBpcre_refcount()\fP 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.
+.P
+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
+\fIadjust\fP 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.
+.P
+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.)
+.
+.
+.SH "MATCHING A PATTERN: THE TRADITIONAL FUNCTION"
+.rs
+.sp
+.B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
+.ti +5n
+.B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
+.ti +5n
+.B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
+.P
+The function \fBpcre_exec()\fP is called to match a subject string against a
+compiled pattern, which is passed in the \fIcode\fP argument. If the
+pattern has been studied, the result of the study should be passed in the
+\fIextra\fP argument. 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
+.\" HTML <a href="#dfamatch">
+.\" </a>
+below
+.\"
+in the section about the \fBpcre_dfa_exec()\fP function.
+.P
+In most applications, the pattern will have been compiled (and optionally
+studied) in the same process that calls \fBpcre_exec()\fP. 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
+.\" HREF
+\fBpcreprecompile\fP
+.\"
+documentation.
+.P
+Here is an example of a simple call to \fBpcre_exec()\fP:
+.sp
+ 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) */
+.
+.\" HTML <a name="extradata"></a>
+.SS "Extra data for \fBpcre_exec()\fR"
+.rs
+.sp
+If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
+data block. The \fBpcre_study()\fP 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 \fBpcre_extra\fP block contains the following
+fields (not necessarily in this order):
+.sp
+ unsigned long int \fIflags\fP;
+ void *\fIstudy_data\fP;
+ unsigned long int \fImatch_limit\fP;
+ unsigned long int \fImatch_limit_recursion\fP;
+ void *\fIcallout_data\fP;
+ const unsigned char *\fItables\fP;
+.sp
+The \fIflags\fP field is a bitmap that specifies which of the other fields
+are set. The flag bits are:
+.sp
+ PCRE_EXTRA_STUDY_DATA
+ PCRE_EXTRA_MATCH_LIMIT
+ PCRE_EXTRA_MATCH_LIMIT_RECURSION
+ PCRE_EXTRA_CALLOUT_DATA
+ PCRE_EXTRA_TABLES
+.sp
+Other flag bits should be set to zero. The \fIstudy_data\fP field is set in the
+\fBpcre_extra\fP block that is returned by \fBpcre_study()\fP, together with
+the appropriate flag bit. You should not set this yourself, but you may add to
+the block by setting the other fields and their corresponding flag bits.
+.P
+The \fImatch_limit\fP 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 the use of nested unlimited repeats.
+.P
+Internally, PCRE uses a function called \fBmatch()\fP which it calls repeatedly
+(sometimes recursively). The limit set by \fImatch_limit\fP 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.
+.P
+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 \fBpcre_exec()\fP with a \fBpcre_extra\fP
+block in which \fImatch_limit\fP is set, and PCRE_EXTRA_MATCH_LIMIT is set in
+the \fIflags\fP field. If the limit is exceeded, \fBpcre_exec()\fP returns
+PCRE_ERROR_MATCHLIMIT.
+.P
+The \fImatch_limit_recursion\fP field is similar to \fImatch_limit\fP, but
+instead of limiting the total number of times that \fBmatch()\fP 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 \fBmatch()\fP are recursive.
+This limit is of use only if it is set smaller than \fImatch_limit\fP.
+.P
+Limiting the recursion depth limits the amount of 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.
+.P
+The default value for \fImatch_limit_recursion\fP can be set when PCRE is
+built; the default default is the same value as the default for
+\fImatch_limit\fP. You can override the default by suppling \fBpcre_exec()\fP
+with a \fBpcre_extra\fP block in which \fImatch_limit_recursion\fP is set, and
+PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the \fIflags\fP field. If the limit
+is exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_RECURSIONLIMIT.
+.P
+The \fIpcre_callout\fP field is used in conjunction with the "callout" feature,
+which is described in the
+.\" HREF
+\fBpcrecallout\fP
+.\"
+documentation.
+.P
+The \fItables\fP field is used to pass a character tables pointer to
+\fBpcre_exec()\fP; this overrides the value that is stored with the compiled
+pattern. A non-NULL value is stored with the compiled pattern only if custom
+tables were supplied to \fBpcre_compile()\fP via its \fItableptr\fP argument.
+If NULL is passed to \fBpcre_exec()\fP using this mechanism, it forces PCRE's
+internal tables to be used. This facility is helpful when re-using patterns
+that have been saved after compiling with an external set of tables, because
+the external tables might be at a different address when \fBpcre_exec()\fP is
+called. See the
+.\" HREF
+\fBpcreprecompile\fP
+.\"
+documentation for a discussion of saving compiled patterns for later use.
+.
+.\" HTML <a name="execoptions"></a>
+.SS "Option bits for \fBpcre_exec()\fP"
+.rs
+.sp
+The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
+zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
+PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
+.sp
+ PCRE_ANCHORED
+.sp
+The PCRE_ANCHORED option limits \fBpcre_exec()\fP 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.
+.sp
+ PCRE_BSR_ANYCRLF
+ PCRE_BSR_UNICODE
+.sp
+These options (which are mutually exclusive) control what the \eR 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.
+.sp
+ PCRE_NEWLINE_CR
+ PCRE_NEWLINE_LF
+ PCRE_NEWLINE_CRLF
+ PCRE_NEWLINE_ANYCRLF
+ PCRE_NEWLINE_ANY
+.sp
+These options override the newline definition that was chosen or defaulted when
+the pattern was compiled. For details, see the description of
+\fBpcre_compile()\fP 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.
+.P
+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.
+.P
+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 "\er\enA" because, after failing at the
+start, it skips both the CR and the LF before retrying. However, the pattern
+[\er\en]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.
+.P
+An explicit match for CR of LF is either a literal appearance of one of those
+characters, or one of the \er or \en escape sequences. Implicit matches such as
+[^X] do not count, nor does \es (which includes CR and LF in the characters
+that it matches).
+.P
+Notwithstanding the above, anomalous effects may still occur when CRLF is a
+valid newline sequence and explicit \er or \en escapes appear in the pattern.
+.sp
+ PCRE_NOTBOL
+.sp
+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 \eA.
+.sp
+ PCRE_NOTEOL
+.sp
+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 \eZ or \ez.
+.sp
+ PCRE_NOTEMPTY
+.sp
+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
+.sp
+ a?b?
+.sp
+is applied to a string not beginning with "a" or "b", it matches the 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".
+.P
+Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
+of a pattern match of the empty string within its \fBsplit()\fP 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 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 \fIpcredemo.c\fP sample program.
+.sp
+ PCRE_NO_UTF8_CHECK
+.sp
+When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
+string is automatically checked when \fBpcre_exec()\fP is subsequently called.
+The value of \fIstartoffset\fP 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
+.\" HTML <a href="pcre.html#utf8strings">
+.\" </a>
+section on UTF-8 support
+.\"
+in the main
+.\" HREF
+\fBpcre\fP
+.\"
+page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_exec()\fP returns
+the error PCRE_ERROR_BADUTF8. If \fIstartoffset\fP contains an invalid value,
+PCRE_ERROR_BADUTF8_OFFSET is returned.
+.P
+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 \fBpcre_exec()\fP. You might want to do this for the second and
+subsequent calls to \fBpcre_exec()\fP 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 \fIstartoffset\fP points to the start of a UTF-8 character. When
+PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
+subject, or a value of \fIstartoffset\fP that does not point to the start of a
+UTF-8 character, is undefined. Your program may crash.
+.sp
+ PCRE_PARTIAL
+.sp
+This option turns on the partial matching feature. If the subject string fails
+to match the pattern, but at some point during the matching process the end of
+the subject was reached (that is, the subject partially matches the pattern and
+the failure to match occurred only because there were not enough subject
+characters), \fBpcre_exec()\fP returns PCRE_ERROR_PARTIAL instead of
+PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
+may appear in the pattern. These are discussed in the
+.\" HREF
+\fBpcrepartial\fP
+.\"
+documentation.
+.
+.SS "The string to be matched by \fBpcre_exec()\fP"
+.rs
+.sp
+The subject string is passed to \fBpcre_exec()\fP as a pointer in
+\fIsubject\fP, a length (in bytes) in \fIlength\fP, and a starting byte offset
+in \fIstartoffset\fP. In UTF-8 mode, the byte offset must point to the start of
+a UTF-8 character. Unlike the pattern string, the subject may contain binary
+zero bytes. 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.
+.P
+A non-zero starting offset is useful when searching for another match in the
+same subject by calling \fBpcre_exec()\fP again after a previous success.
+Setting \fIstartoffset\fP 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
+.sp
+ \eBiss\eB
+.sp
+which finds occurrences of "iss" in the middle of words. (\eB matches only if
+the current position in the subject is not a word boundary.) When applied to
+the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
+occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
+subject, namely "issipi", it does not match, because \eB is always false at the
+start of the subject, which is deemed to be a word boundary. However, if
+\fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
+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.
+.P
+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.
+.
+.SS "How \fBpcre_exec()\fP returns captured substrings"
+.rs
+.sp
+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.
+.P
+Captured substrings are returned to the caller via a vector of integers whose
+address is passed in \fIovector\fP. The number of elements in the vector is
+passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP: this
+argument is NOT the size of \fIovector\fP in bytes.
+.P
+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 \fBpcre_exec()\fP while matching capturing subpatterns,
+and is not available for passing back information. The number passed in
+\fIovecsize\fP should always be a multiple of three. If it is not, it is
+rounded down.
+.P
+When a match is successful, information about captured substrings is returned
+in pairs of integers, starting at the beginning of \fIovector\fP, and
+continuing up to two-thirds of its length at the most. The first element of
+each pair is set to the byte offset of the first character in a substring, and
+the second is set to the byte offset of the first character after the end of a
+substring. \fBNote\fP: these values are always byte offsets, even in UTF-8
+mode. They are not character counts.
+.P
+The first pair of integers, \fIovector[0]\fP and \fIovector[1]\fP, 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
+\fBpcre_exec()\fP 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.
+.P
+If a capturing subpattern is matched repeatedly, it is the last portion of the
+string that it matched that is returned.
+.P
+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 the substring offsets are not of interest,
+\fBpcre_exec()\fP may be called with \fIovector\fP passed as NULL and
+\fIovecsize\fP as zero. However, if the pattern contains back references and
+the \fIovector\fP 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 \fIovector\fP.
+.P
+The \fBpcre_info()\fP function can be used to find out how many capturing
+subpatterns there are in a compiled pattern. The smallest size for
+\fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
+the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
+.P
+It is possible for capturing subpattern number \fIn+1\fP to match some part of
+the subject when subpattern \fIn\fP 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.
+.P
+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. However, you can refer to the offsets for the second and third
+capturing subpatterns if you wish (assuming the vector is large enough, of
+course).
+.P
+Some convenience functions are provided for extracting the captured substrings
+as separate strings. These are described below.
+.
+.\" HTML <a name="errorlist"></a>
+.SS "Error return values from \fBpcre_exec()\fP"
+.rs
+.sp
+If \fBpcre_exec()\fP fails, it returns a negative number. The following are
+defined in the header file:
+.sp
+ PCRE_ERROR_NOMATCH (-1)
+.sp
+The subject string did not match the pattern.
+.sp
+ PCRE_ERROR_NULL (-2)
+.sp
+Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
+NULL and \fIovecsize\fP was not zero.
+.sp
+ PCRE_ERROR_BADOPTION (-3)
+.sp
+An unrecognized bit was set in the \fIoptions\fP argument.
+.sp
+ PCRE_ERROR_BADMAGIC (-4)
+.sp
+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.
+.sp
+ PCRE_ERROR_UNKNOWN_OPCODE (-5)
+.sp
+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.
+.sp
+ PCRE_ERROR_NOMEMORY (-6)
+.sp
+If a pattern contains back references, but the \fIovector\fP that is passed to
+\fBpcre_exec()\fP 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 \fBpcre_malloc()\fP fails, this error is given. The memory is
+automatically freed at the end of matching.
+.sp
+ PCRE_ERROR_NOSUBSTRING (-7)
+.sp
+This error is used by the \fBpcre_copy_substring()\fP,
+\fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
+below). It is never returned by \fBpcre_exec()\fP.
+.sp
+ PCRE_ERROR_MATCHLIMIT (-8)
+.sp
+The backtracking limit, as specified by the \fImatch_limit\fP field in a
+\fBpcre_extra\fP structure (or defaulted) was reached. See the description
+above.
+.sp
+ PCRE_ERROR_CALLOUT (-9)
+.sp
+This error is never generated by \fBpcre_exec()\fP itself. It is provided for
+use by callout functions that want to yield a distinctive error code. See the
+.\" HREF
+\fBpcrecallout\fP
+.\"
+documentation for details.
+.sp
+ PCRE_ERROR_BADUTF8 (-10)
+.sp
+A string that contains an invalid UTF-8 byte sequence was passed as a subject.
+.sp
+ PCRE_ERROR_BADUTF8_OFFSET (-11)
+.sp
+The UTF-8 byte sequence that was passed as a subject was valid, but the value
+of \fIstartoffset\fP did not point to the beginning of a UTF-8 character.
+.sp
+ PCRE_ERROR_PARTIAL (-12)
+.sp
+The subject string did not match, but it did match partially. See the
+.\" HREF
+\fBpcrepartial\fP
+.\"
+documentation for details of partial matching.
+.sp
+ PCRE_ERROR_BADPARTIAL (-13)
+.sp
+The PCRE_PARTIAL option was used with a compiled pattern containing items that
+are not supported for partial matching. See the
+.\" HREF
+\fBpcrepartial\fP
+.\"
+documentation for details of partial matching.
+.sp
+ PCRE_ERROR_INTERNAL (-14)
+.sp
+An unexpected internal error has occurred. This error could be caused by a bug
+in PCRE or by overwriting of the compiled pattern.
+.sp
+ PCRE_ERROR_BADCOUNT (-15)
+.sp
+This error is given if the value of the \fIovecsize\fP argument is negative.
+.sp
+ PCRE_ERROR_RECURSIONLIMIT (-21)
+.sp
+The internal recursion limit, as specified by the \fImatch_limit_recursion\fP
+field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
+description above.
+.sp
+ PCRE_ERROR_BADNEWLINE (-23)
+.sp
+An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
+.P
+Error numbers -16 to -20 and -22 are not used by \fBpcre_exec()\fP.
+.
+.
+.SH "EXTRACTING CAPTURED SUBSTRINGS BY NUMBER"
+.rs
+.sp
+.B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
+.ti +5n
+.B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
+.ti +5n
+.B int \fIbuffersize\fP);
+.PP
+.B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
+.ti +5n
+.B int \fIstringcount\fP, int \fIstringnumber\fP,
+.ti +5n
+.B const char **\fIstringptr\fP);
+.PP
+.B int pcre_get_substring_list(const char *\fIsubject\fP,
+.ti +5n
+.B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
+.PP
+Captured substrings can be accessed directly by using the offsets returned by
+\fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
+\fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
+\fBpcre_get_substring_list()\fP 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.
+.P
+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 \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP.
+Unfortunately, the interface to \fBpcre_get_substring_list()\fP is not adequate
+for handling strings containing binary zeros, because the end of the final
+string is not independently indicated.
+.P
+The first three arguments are the same for all three of these functions:
+\fIsubject\fP is the subject string that has just been successfully matched,
+\fIovector\fP is a pointer to the vector of integer offsets that was passed to
+\fBpcre_exec()\fP, and \fIstringcount\fP 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 \fBpcre_exec()\fP if it is greater
+than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
+space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
+number of elements in the vector divided by three.
+.P
+The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
+extract a single substring, whose number is given as \fIstringnumber\fP. A
+value of zero extracts the substring that matched the entire pattern, whereas
+higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
+the string is placed in \fIbuffer\fP, whose length is given by
+\fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
+obtained via \fBpcre_malloc\fP, and its address is returned via
+\fIstringptr\fP. The yield of the function is the length of the string, not
+including the terminating zero, or one of these error codes:
+.sp
+ PCRE_ERROR_NOMEMORY (-6)
+.sp
+The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
+memory failed for \fBpcre_get_substring()\fP.
+.sp
+ PCRE_ERROR_NOSUBSTRING (-7)
+.sp
+There is no substring whose number is \fIstringnumber\fP.
+.P
+The \fBpcre_get_substring_list()\fP 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 \fBpcre_malloc\fP. The address of the memory block
+is returned via \fIlistptr\fP, 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
+.sp
+ PCRE_ERROR_NOMEMORY (-6)
+.sp
+if the attempt to get the memory block failed.
+.P
+When any of these functions encounter a substring that is unset, which can
+happen when capturing subpattern number \fIn+1\fP matches some part of the
+subject, but subpattern \fIn\fP 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 \fIovector\fP, which is negative for unset
+substrings.
+.P
+The two convenience functions \fBpcre_free_substring()\fP and
+\fBpcre_free_substring_list()\fP can be used to free the memory returned by
+a previous call of \fBpcre_get_substring()\fP or
+\fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
+the function pointed to by \fBpcre_free\fP, 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
+\fBpcre_free\fP directly; it is for these cases that the functions are
+provided.
+.
+.
+.SH "EXTRACTING CAPTURED SUBSTRINGS BY NAME"
+.rs
+.sp
+.B int pcre_get_stringnumber(const pcre *\fIcode\fP,
+.ti +5n
+.B const char *\fIname\fP);
+.PP
+.B int pcre_copy_named_substring(const pcre *\fIcode\fP,
+.ti +5n
+.B const char *\fIsubject\fP, int *\fIovector\fP,
+.ti +5n
+.B int \fIstringcount\fP, const char *\fIstringname\fP,
+.ti +5n
+.B char *\fIbuffer\fP, int \fIbuffersize\fP);
+.PP
+.B int pcre_get_named_substring(const pcre *\fIcode\fP,
+.ti +5n
+.B const char *\fIsubject\fP, int *\fIovector\fP,
+.ti +5n
+.B int \fIstringcount\fP, const char *\fIstringname\fP,
+.ti +5n
+.B const char **\fIstringptr\fP);
+.PP
+To extract a substring by name, you first have to find associated number.
+For example, for this pattern
+.sp
+ (a+)b(?<xxx>\ed+)...
+.sp
+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 \fBpcre_get_stringnumber()\fP. 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.
+.P
+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.
+.P
+Most of the arguments of \fBpcre_copy_named_substring()\fP and
+\fBpcre_get_named_substring()\fP 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:
+.P
+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.
+.P
+These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
+then call \fBpcre_copy_substring()\fP or \fBpcre_get_substring()\fP, as
+appropriate. \fBNOTE:\fP If PCRE_DUPNAMES is set and there are duplicate names,
+the behaviour may not be what you want (see the next section).
+.
+.
+.SH "DUPLICATE SUBPATTERN NAMES"
+.rs
+.sp
+.B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
+.ti +5n
+.B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
+.PP
+When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
+are not required to be unique. 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
+.\" HREF
+\fBpcrepattern\fP
+.\"
+documentation.
+.P
+When duplicates are present, \fBpcre_copy_named_substring()\fP and
+\fBpcre_get_named_substring()\fP 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 \fBpcre_get_stringnumber()\fP function
+returns one of the numbers that are associated with the name, but it is not
+defined which it is.
+.P
+If you want to get full details of all captured substrings for a given name,
+you must use the \fBpcre_get_stringtable_entries()\fP 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 \fIInformation about a pattern\fP.
+Given all the relevant entries for the name, you can extract each of their
+numbers, and hence the captured data, if any.
+.
+.
+.SH "FINDING ALL POSSIBLE MATCHES"
+.rs
+.sp
+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
+.\" HREF
+\fBpcrecallout\fP
+.\"
+documentation.
+.P
+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 \fBpcre_exec()\fP to backtrack and try
+other alternatives. Ultimately, when it runs out of matches, \fBpcre_exec()\fP
+will yield PCRE_ERROR_NOMATCH.
+.
+.
+.\" HTML <a name="dfamatch"></a>
+.SH "MATCHING A PATTERN: THE ALTERNATIVE FUNCTION"
+.rs
+.sp
+.B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
+.ti +5n
+.B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
+.ti +5n
+.B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
+.ti +5n
+.B int *\fIworkspace\fP, int \fIwscount\fP);
+.P
+The function \fBpcre_dfa_exec()\fP 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, see
+the
+.\" HREF
+\fBpcrematching\fP
+.\"
+documentation.
+.P
+The arguments for the \fBpcre_dfa_exec()\fP function are the same as for
+\fBpcre_exec()\fP, plus two extras. The \fIovector\fP argument is used in a
+different way, and this is described below. The other common arguments are used
+in the same way as for \fBpcre_exec()\fP, so their description is not repeated
+here.
+.P
+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.
+.P
+Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
+.sp
+ 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) */
+.
+.SS "Option bits for \fBpcre_dfa_exec()\fP"
+.rs
+.sp
+The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
+zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
+PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL,
+PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last three of these are
+the same as for \fBpcre_exec()\fP, so their description is not repeated here.
+.sp
+ PCRE_PARTIAL
+.sp
+This has the same general effect as it does for \fBpcre_exec()\fP, but the
+details are slightly different. When PCRE_PARTIAL is set for
+\fBpcre_dfa_exec()\fP, 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 provided the partial match is set as the first
+matching string.
+.sp
+ PCRE_DFA_SHORTEST
+.sp
+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.
+.sp
+ PCRE_DFA_RESTART
+.sp
+When \fBpcre_dfa_exec()\fP is called with the PCRE_PARTIAL option, and 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 \fIworkspace\fP and
+\fIwscount\fP 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
+.\" HREF
+\fBpcrepartial\fP
+.\"
+documentation.
+.
+.SS "Successful returns from \fBpcre_dfa_exec()\fP"
+.rs
+.sp
+When \fBpcre_dfa_exec()\fP 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
+.sp
+ <.*>
+.sp
+is matched against the string
+.sp
+ This is <something> <something else> <something further> no more
+.sp
+the three matched strings are
+.sp
+ <something>
+ <something> <something else>
+ <something> <something else> <something further>
+.sp
+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
+\fIovector\fP. 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 \fBpcre_exec()\fP
+returns data, even though the meaning of the strings is different.)
+.P
+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
+\fIovector\fP, the yield of the function is zero, and the vector is filled with
+the longest matches.
+.
+.SS "Error returns from \fBpcre_dfa_exec()\fP"
+.rs
+.sp
+The \fBpcre_dfa_exec()\fP function returns a negative number when it fails.
+Many of the errors are the same as for \fBpcre_exec()\fP, and these are
+described
+.\" HTML <a href="#errorlist">
+.\" </a>
+above.
+.\"
+There are in addition the following errors that are specific to
+\fBpcre_dfa_exec()\fP:
+.sp
+ PCRE_ERROR_DFA_UITEM (-16)
+.sp
+This return is given if \fBpcre_dfa_exec()\fP encounters an item in the pattern
+that it does not support, for instance, the use of \eC or a back reference.
+.sp
+ PCRE_ERROR_DFA_UCOND (-17)
+.sp
+This return is given if \fBpcre_dfa_exec()\fP 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.
+.sp
+ PCRE_ERROR_DFA_UMLIMIT (-18)
+.sp
+This return is given if \fBpcre_dfa_exec()\fP is called with an \fIextra\fP
+block that contains a setting of the \fImatch_limit\fP field. This is not
+supported (it is meaningless).
+.sp
+ PCRE_ERROR_DFA_WSSIZE (-19)
+.sp
+This return is given if \fBpcre_dfa_exec()\fP runs out of space in the
+\fIworkspace\fP vector.
+.sp
+ PCRE_ERROR_DFA_RECURSE (-20)
+.sp
+When a recursive subpattern is processed, the matching function calls itself
+recursively, using private vectors for \fIovector\fP and \fIworkspace\fP. 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.
+.
+.
+.SH "SEE ALSO"
+.rs
+.sp
+\fBpcrebuild\fP(3), \fBpcrecallout\fP(3), \fBpcrecpp(3)\fP(3),
+\fBpcrematching\fP(3), \fBpcrepartial\fP(3), \fBpcreposix\fP(3),
+\fBpcreprecompile\fP(3), \fBpcresample\fP(3), \fBpcrestack\fP(3).
+.
+.
+.SH AUTHOR
+.rs
+.sp
+.nf
+Philip Hazel
+University Computing Service
+Cambridge CB2 3QH, England.
+.fi
+.
+.
+.SH REVISION
+.rs
+.sp
+.nf
+Last updated: 24 August 2008
+Copyright (c) 1997-2008 University of Cambridge.
+.fi