diff options
Diffstat (limited to 'doc/html/pcreapi.html')
| -rw-r--r-- | doc/html/pcreapi.html | 1260 |
1 files changed, 1260 insertions, 0 deletions
diff --git a/doc/html/pcreapi.html b/doc/html/pcreapi.html new file mode 100644 index 0000000..3bc71b1 --- /dev/null +++ b/doc/html/pcreapi.html @@ -0,0 +1,1260 @@ +<html> +<head> +<title>pcreapi specification</title> +</head> +<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> +This HTML document has been 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.<br> +<ul> +<li><a name="TOC1" href="#SEC1">SYNOPSIS OF PCRE API</a> +<li><a name="TOC2" href="#SEC2">PCRE API</a> +<li><a name="TOC3" href="#SEC3">MULTITHREADING</a> +<li><a name="TOC4" href="#SEC4">CHECKING BUILD-TIME OPTIONS</a> +<li><a name="TOC5" href="#SEC5">COMPILING A PATTERN</a> +<li><a name="TOC6" href="#SEC6">STUDYING A PATTERN</a> +<li><a name="TOC7" href="#SEC7">LOCALE SUPPORT</a> +<li><a name="TOC8" href="#SEC8">INFORMATION ABOUT A PATTERN</a> +<li><a name="TOC9" href="#SEC9">OBSOLETE INFO FUNCTION</a> +<li><a name="TOC10" href="#SEC10">MATCHING A PATTERN</a> +<li><a name="TOC11" href="#SEC11">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a> +<li><a name="TOC12" href="#SEC12">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a> +</ul> +<br><a name="SEC1" href="#TOC1">SYNOPSIS OF PCRE API</a><br> +<P> +<b>#include <pcre.h></b> +</P> +<P> +<b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b> +<b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b> +<b>const unsigned char *<i>tableptr</i>);</b> +</P> +<P> +<b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b> +<b>const char **<i>errptr</i>);</b> +</P> +<P> +<b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b> +<b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b> +<b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b> +</P> +<P> +<b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b> +<b>const char *<i>subject</i>, int *<i>ovector</i>,</b> +<b>int <i>stringcount</i>, const char *<i>stringname</i>,</b> +<b>char *<i>buffer</i>, int <i>buffersize</i>);</b> +</P> +<P> +<b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b> +<b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b> +<b>int <i>buffersize</i>);</b> +</P> +<P> +<b>int pcre_get_named_substring(const pcre *<i>code</i>,</b> +<b>const char *<i>subject</i>, int *<i>ovector</i>,</b> +<b>int <i>stringcount</i>, const char *<i>stringname</i>,</b> +<b>const char **<i>stringptr</i>);</b> +</P> +<P> +<b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b> +<b>const char *<i>name</i>);</b> +</P> +<P> +<b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b> +<b>int <i>stringcount</i>, int <i>stringnumber</i>,</b> +<b>const char **<i>stringptr</i>);</b> +</P> +<P> +<b>int pcre_get_substring_list(const char *<i>subject</i>,</b> +<b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b> +</P> +<P> +<b>void pcre_free_substring(const char *<i>stringptr</i>);</b> +</P> +<P> +<b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b> +</P> +<P> +<b>const unsigned char *pcre_maketables(void);</b> +</P> +<P> +<b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b> +<b>int <i>what</i>, void *<i>where</i>);</b> +</P> +<P> +<b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b> +<b>*<i>firstcharptr</i>);</b> +</P> +<P> +<b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b> +</P> +<P> +<b>char *pcre_version(void);</b> +</P> +<P> +<b>void *(*pcre_malloc)(size_t);</b> +</P> +<P> +<b>void (*pcre_free)(void *);</b> +</P> +<P> +<b>int (*pcre_callout)(pcre_callout_block *);</b> +</P> +<br><a name="SEC2" href="#TOC1">PCRE API</a><br> +<P> +PCRE has its own native API, which is described in this document. There is also +a set of wrapper functions that correspond to the POSIX regular expression API. +These are described in the <b>pcreposix</b> documentation. +</P> +<P> +The native API function prototypes are defined in the header file <b>pcre.h</b>, +and on Unix systems the library itself is called <b>libpcre.a</b>, so can be +accessed by adding <b>-lpcre</b> to the command for linking an application which +calls it. 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. +</P> +<P> +The functions <b>pcre_compile()</b>, <b>pcre_study()</b>, and <b>pcre_exec()</b> +are used for compiling and matching regular expressions. A sample program that +demonstrates the simplest way of using them is given in the file +<i>pcredemo.c</i>. The <b>pcresample</b> documentation describes how to run it. +</P> +<P> +There are convenience functions for extracting captured substrings from a +matched subject string. They are: +</P> +<P> +<pre> + <b>pcre_copy_substring()</b> + <b>pcre_copy_named_substring()</b> + <b>pcre_get_substring()</b> + <b>pcre_get_named_substring()</b> + <b>pcre_get_substring_list()</b> +</PRE> +</P> +<P> +<b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also +provided, to free the memory used for extracted strings. +</P> +<P> +The function <b>pcre_maketables()</b> is used (optionally) to build a set of +character tables in the current locale for passing to <b>pcre_compile()</b>. +</P> +<P> +The function <b>pcre_fullinfo()</b> is used to find out information about a +compiled pattern; <b>pcre_info()</b> is an obsolete version which returns only +some of the available information, but is retained for backwards compatibility. +The function <b>pcre_version()</b> returns a pointer to a string containing the +version of PCRE and its date of release. +</P> +<P> +The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain +the entry points of the standard <b>malloc()</b> and <b>free()</b> 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> +<P> +The global variable <b>pcre_callout</b> 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 <b>pcrecallout</b> +documentation. +</P> +<br><a name="SEC3" href="#TOC1">MULTITHREADING</a><br> +<P> +The PCRE functions can be used in multi-threading applications, with the +proviso that the memory management functions pointed to by <b>pcre_malloc</b> +and <b>pcre_free</b>, and the callout function pointed to by <b>pcre_callout</b>, +are shared by all threads. +</P> +<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. +</P> +<br><a name="SEC4" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br> +<P> +<b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b> +</P> +<P> +The function <b>pcre_config()</b> makes it possible for a PCRE client to +discover which optional features have been compiled into the PCRE library. The +<a href="pcrebuild.html"><b>pcrebuild</b></a> +documentation has more details about these optional features. +</P> +<P> +The first argument for <b>pcre_config()</b> 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: +</P> +<P> +<pre> + PCRE_CONFIG_UTF8 +</PRE> +</P> +<P> +The output is an integer that is set to one if UTF-8 support is available; +otherwise it is set to zero. +</P> +<P> +<pre> + PCRE_CONFIG_NEWLINE +</PRE> +</P> +<P> +The output is an integer that is set to the value of the code that is used for +the newline character. It is either linefeed (10) or carriage return (13), and +should normally be the standard character for your operating system. +</P> +<P> +<pre> + PCRE_CONFIG_LINK_SIZE +</PRE> +</P> +<P> +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. +</P> +<P> +<pre> + PCRE_CONFIG_POSIX_MALLOC_THRESHOLD +</PRE> +</P> +<P> +The output is an integer that contains the threshold above which the POSIX +interface uses <b>malloc()</b> for output vectors. Further details are given in +the <b>pcreposix</b> documentation. +</P> +<P> +<pre> + PCRE_CONFIG_MATCH_LIMIT +</PRE> +</P> +<P> +The output is an integer that gives the default limit for the number of +internal matching function calls in a <b>pcre_exec()</b> execution. Further +details are given with <b>pcre_exec()</b> below. +</P> +<br><a name="SEC5" href="#TOC1">COMPILING A PATTERN</a><br> +<P> +<b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b> +<b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b> +<b>const unsigned char *<i>tableptr</i>);</b> +</P> +<P> +The function <b>pcre_compile()</b> is called to compile a pattern into an +internal form. The pattern is a C string terminated by a binary zero, and +is passed in the argument <i>pattern</i>. A pointer to a single block of memory +that is obtained via <b>pcre_malloc</b> is returned. This contains the compiled +code and related data. The <b>pcre</b> 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 when it is no longer required. +</P> +<P> +Although the compiled code of a PCRE regex is relocatable, that is, it does not +depend on memory location, the complete <b>pcre</b> data block is not +fully relocatable, because it contains a copy of the <i>tableptr</i> argument, +which is an address (see below). +</P> +<P> +The <i>options</i> argument contains independent bits that affect the +compilation. It should be zero if no options are required. Some of the options, +in particular, those that are compatible with Perl, can also be set and unset +from within the pattern (see the detailed description of regular expressions +in the <b>pcrepattern</b> documentation). For these options, the contents of the +<i>options</i> argument specifies their initial settings at the start of +compilation and execution. The PCRE_ANCHORED option can be set at the time of +matching as well as at compile time. +</P> +<P> +If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately. +Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns +NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual +error message. The offset from the start of the pattern to the character where +the error was discovered is placed in the variable pointed to by +<i>erroffset</i>, which must not be NULL. If it is, an immediate error is given. +</P> +<P> +If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of +character tables which are built when it is compiled, using the default C +locale. Otherwise, <i>tableptr</i> must be the result of a call to +<b>pcre_maketables()</b>. See the section on locale support below. +</P> +<P> +This code fragment shows a typical straightforward call to <b>pcre_compile()</b>: +</P> +<P> +<pre> + 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 */ +</PRE> +</P> +<P> +The following option bits are defined: +</P> +<P> +<pre> + PCRE_ANCHORED +</PRE> +</P> +<P> +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 which 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. +</P> +<P> +<pre> + PCRE_CASELESS +</PRE> +</P> +<P> +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. +</P> +<P> +<pre> + PCRE_DOLLAR_ENDONLY +</PRE> +</P> +<P> +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 the final character if it is a newline (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. +</P> +<P> +<pre> + PCRE_DOTALL +</PRE> +</P> +<P> +If this bit is set, a dot metacharater in the pattern matches all characters, +including newlines. Without it, newlines are excluded. 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 a newline +character, independent of the setting of this option. +</P> +<P> +<pre> + PCRE_EXTENDED +</PRE> +</P> +<P> +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 character, +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> +<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. +</P> +<P> +<pre> + PCRE_EXTRA +</PRE> +</P> +<P> +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. There are at present no other features +controlled by this option. It can also be set by a (?X) option setting within a +pattern. +</P> +<P> +<pre> + PCRE_MULTILINE +</PRE> +</P> +<P> +By default, PCRE treats the subject string as consisting of a single "line" of +characters (even if it actually contains several 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> +<P> +When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs +match immediately following or immediately before any newline 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 "\n" characters in a subject string, or no +occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect. +</P> +<P> +<pre> + PCRE_NO_AUTO_CAPTURE +</PRE> +</P> +<P> +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. +</P> +<P> +<pre> + PCRE_UNGREEDY +</PRE> +</P> +<P> +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. +</P> +<P> +<pre> + PCRE_UTF8 +</PRE> +</P> +<P> +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 if PCRE has been 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 +<a href="pcre.html#utf8support">section on UTF-8 support</a> +in the main +<a href="pcre.html"><b>pcre</b></a> +page. +</P> +<br><a name="SEC6" href="#TOC1">STUDYING A PATTERN</a><br> +<P> +<b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b> +<b>const char **<i>errptr</i>);</b> +</P> +<P> +When a 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 <b>pcre_study()</b> takes a pointer to a compiled pattern as its first +argument. If studing the pattern produces additional information that will help +speed up matching, <b>pcre_study()</b> returns a pointer to a <b>pcre_extra</b> +block, in which the <i>study_data</i> field points to the results of the study. +</P> +<P> +The returned value from a <b>pcre_study()</b> can be passed directly to +<b>pcre_exec()</b>. However, the <b>pcre_extra</b> block also contains other +fields that can be set by the caller before the block is passed; these are +described below. If studying the pattern does not produce any additional +information, <b>pcre_study()</b> returns NULL. In that circumstance, if the +calling program wants to pass some of the other fields to <b>pcre_exec()</b>, it +must set up its own <b>pcre_extra</b> block. +</P> +<P> +The second argument contains option bits. At present, no options are defined +for <b>pcre_study()</b>, and this argument should always be zero. +</P> +<P> +The third argument for <b>pcre_study()</b> 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 points to a textual error message. You should +therefore test the error pointer for NULL after calling <b>pcre_study()</b>, to +be sure that it has run successfully. +</P> +<P> +This is a typical call to <b>pcre_study</b>(): +</P> +<P> +<pre> + pcre_extra *pe; + pe = pcre_study( + re, /* result of pcre_compile() */ + 0, /* no options exist */ + &error); /* set to NULL or points to a message */ +</PRE> +</P> +<P> +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 +characters is created. +</P> +<a name="localesupport"></a><br><a name="SEC7" href="#TOC1">LOCALE SUPPORT</a><br> +<P> +PCRE handles caseless matching, and determines whether characters are letters, +digits, or whatever, by reference to a set of tables. When running in UTF-8 +mode, this applies only to characters with codes less than 256. The library +contains a default set of tables that is created in the default C locale when +PCRE is compiled. This is used when the final argument of <b>pcre_compile()</b> +is NULL, and is sufficient for many applications. +</P> +<P> +An alternative set of tables can, however, be supplied. Such tables are built +by calling the <b>pcre_maketables()</b> function, which has no arguments, in the +relevant locale. The result can then be passed to <b>pcre_compile()</b> as often +as necessary. For example, to build and use tables that are appropriate for the +French locale (where accented characters with codes greater than 128 are +treated as letters), the following code could be used: +</P> +<P> +<pre> + setlocale(LC_CTYPE, "fr"); + tables = pcre_maketables(); + re = pcre_compile(..., tables); +</PRE> +</P> +<P> +The tables are built in memory that is obtained via <b>pcre_malloc</b>. The +pointer that is passed to <b>pcre_compile</b> is saved with the compiled +pattern, and the same tables are used via this pointer by <b>pcre_study()</b> +and <b>pcre_exec()</b>. Thus, for any single pattern, compilation, studying and +matching all happen in the same locale, but different patterns can be compiled +in different locales. It is the caller's responsibility to ensure that the +memory containing the tables remains available for as long as it is needed. +</P> +<br><a name="SEC8" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br> +<P> +<b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b> +<b>int <i>what</i>, void *<i>where</i>);</b> +</P> +<P> +The <b>pcre_fullinfo()</b> function returns information about a compiled +pattern. It replaces the obsolete <b>pcre_info()</b> function, which is +nevertheless retained for backwards compability (and is documented below). +</P> +<P> +The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled +pattern. The second argument is the result of <b>pcre_study()</b>, 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: +</P> +<P> +<pre> + PCRE_ERROR_NULL the argument <i>code</i> was NULL + the argument <i>where</i> was NULL + PCRE_ERROR_BADMAGIC the "magic number" was not found + PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid +</PRE> +</P> +<P> +Here is a typical call of <b>pcre_fullinfo()</b>, to obtain the length of the +compiled pattern: +</P> +<P> +<pre> + int rc; + unsigned long int 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 */ +</PRE> +</P> +<P> +The possible values for the third argument are defined in <b>pcre.h</b>, and are +as follows: +</P> +<P> +<pre> + PCRE_INFO_BACKREFMAX +</PRE> +</P> +<P> +Return the number of the highest back reference in the pattern. The fourth +argument should point to an <b>int</b> variable. Zero is returned if there are +no back references. +</P> +<P> +<pre> + PCRE_INFO_CAPTURECOUNT +</PRE> +</P> +<P> +Return the number of capturing subpatterns in the pattern. The fourth argument +should point to an \fbint\fR variable. +</P> +<P> +<pre> + PCRE_INFO_FIRSTBYTE +</PRE> +</P> +<P> +Return information about the first byte of any matched string, for a +non-anchored pattern. (This option used to be called PCRE_INFO_FIRSTCHAR; the +old name is still recognized for backwards compatibility.) +</P> +<P> +If there is a fixed first byte, e.g. from a pattern such as (cat|cow|coyote), +it is returned in the integer pointed to by <i>where</i>. Otherwise, if either +</P> +<P> +(a) the pattern was compiled with the PCRE_MULTILINE option, and every branch +starts with "^", or +</P> +<P> +(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set +(if it were set, the pattern would be anchored), +</P> +<P> +-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. +</P> +<P> +<pre> + PCRE_INFO_FIRSTTABLE +</PRE> +</P> +<P> +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 <b>unsigned char *</b> variable. +</P> +<P> +<pre> + PCRE_INFO_LASTLITERAL +</PRE> +</P> +<P> +For a non-anchored pattern, return the value of the rightmost literal byte +which must exist in any matched string, other than at its start. The fourth +argument should point to an <b>int</b> variable. If there is no such byte, or if +the pattern is anchored, -1 is returned. For example, for the pattern +/a\d+z\d+/ the returned value is 'z'. +</P> +<P> +<pre> + PCRE_INFO_NAMECOUNT + PCRE_INFO_NAMEENTRYSIZE + PCRE_INFO_NAMETABLE +</PRE> +</P> +<P> +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 a number. A caller that wants to extract data from a named subpattern +must convert the name to a number in order to access the correct pointers in +the output vector (described with <b>pcre_exec()</b> below). In order to do +this, it must first use these three values to obtain the name-to-number mapping +table for the pattern. +</P> +<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 <b>int</b> 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 <b>char</b>). 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. For example, consider the following pattern (assume +PCRE_EXTENDED is set, so white space - including newlines - is ignored): +</P> +<P> +<pre> + (?P<date> (?P<year>(\d\d)?\d\d) - + (?P<month>\d\d) - (?P<day>\d\d) ) +</PRE> +</P> +<P> +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 hex, and undefined bytes shown as ??: +</P> +<P> +<pre> + 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 ?? +</PRE> +</P> +<P> +When writing code to extract data from named subpatterns, remember that the +length of each entry may be different for each compiled pattern. +</P> +<P> +<pre> + PCRE_INFO_OPTIONS +</PRE> +</P> +<P> +Return a copy of the options with which the pattern was compiled. The fourth +argument should point to an <b>unsigned long int</b> variable. These option bits +are those specified in the call to <b>pcre_compile()</b>, modified by any +top-level option settings within the pattern itself. +</P> +<P> +A pattern is automatically anchored by PCRE if all of its top-level +alternatives begin with one of the following: +</P> +<P> +<pre> + ^ 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 +</PRE> +</P> +<P> +For such patterns, the PCRE_ANCHORED bit is set in the options returned by +<b>pcre_fullinfo()</b>. +</P> +<P> +<pre> + PCRE_INFO_SIZE +</PRE> +</P> +<P> +Return the size of the compiled pattern, that is, the value that was passed as +the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to +place the compiled data. The fourth argument should point to a <b>size_t</b> +variable. +</P> +<P> +<pre> + PCRE_INFO_STUDYSIZE +</PRE> +</P> +<P> +Returns the size of the data block pointed to by the <i>study_data</i> field in +a <b>pcre_extra</b> block. That is, it is the value that was passed to +<b>pcre_malloc()</b> when PCRE was getting memory into which to place the data +created by <b>pcre_study()</b>. The fourth argument should point to a +<b>size_t</b> variable. +</P> +<br><a name="SEC9" href="#TOC1">OBSOLETE INFO FUNCTION</a><br> +<P> +<b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b> +<b>*<i>firstcharptr</i>);</b> +</P> +<P> +The <b>pcre_info()</b> function is now obsolete because its interface is too +restrictive to return all the available data about a compiled pattern. New +programs should use <b>pcre_fullinfo()</b> instead. The yield of +<b>pcre_info()</b> is the number of capturing subpatterns, or one of the +following negative numbers: +</P> +<P> +<pre> + PCRE_ERROR_NULL the argument <i>code</i> was NULL + PCRE_ERROR_BADMAGIC the "magic number" was not found +</PRE> +</P> +<P> +If the <i>optptr</i> 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> +<P> +If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL, +it is used to pass back information about the first character of any matched +string (see PCRE_INFO_FIRSTBYTE above). +</P> +<br><a name="SEC10" href="#TOC1">MATCHING A PATTERN</a><br> +<P> +<b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b> +<b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b> +<b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b> +</P> +<P> +The function <b>pcre_exec()</b> is called to match a subject string against a +pre-compiled pattern, which is passed in the <i>code</i> argument. If the +pattern has been studied, the result of the study should be passed in the +<i>extra</i> argument. +</P> +<P> +Here is an example of a simple call to <b>pcre_exec()</b>: +</P> +<P> +<pre> + 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 for substring information */ + 30); /* number of elements in the vector */ +</PRE> +</P> +<P> +If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b> +data block. The <b>pcre_study()</b> 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 fields in the block are as follows: +</P> +<P> +<pre> + unsigned long int <i>flags</i>; + void *<i>study_data</i>; + unsigned long int <i>match_limit</i>; + void *<i>callout_data</i>; +</PRE> +</P> +<P> +The <i>flags</i> field is a bitmap that specifies which of the other fields +are set. The flag bits are: +</P> +<P> +<pre> + PCRE_EXTRA_STUDY_DATA + PCRE_EXTRA_MATCH_LIMIT + PCRE_EXTRA_CALLOUT_DATA +</PRE> +</P> +<P> +Other flag bits should be set to zero. The <i>study_data</i> field is set in the +<b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with +the appropriate flag bit. You should not set this yourself, but you can add to +the block by setting the other fields. +</P> +<P> +The <i>match_limit</i> 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. Internally, PCRE uses a +function called <b>match()</b> which it calls repeatedly (sometimes +recursively). The limit is imposed on the number of times this function is +called during a match, which has the effect of limiting the amount of recursion +and backtracking that can take place. For patterns that are not anchored, the +count starts from zero for each position in the subject string. +</P> +<P> +The default limit for the library can be set when PCRE is built; the default +default is 10 million, which handles all but the most extreme cases. You can +reduce the default by suppling <b>pcre_exec()</b> with a \fRpcre_extra\fR block +in which <i>match_limit</i> is set to a smaller value, and +PCRE_EXTRA_MATCH_LIMIT is set in the <i>flags</i> field. If the limit is +exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_MATCHLIMIT. +</P> +<P> +The <i>pcre_callout</i> field is used in conjunction with the "callout" feature, +which is described in the <b>pcrecallout</b> documentation. +</P> +<P> +The PCRE_ANCHORED option can be passed in the <i>options</i> argument, whose +unused bits must be zero. This limits <b>pcre_exec()</b> to matching at the +first matching position. However, 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. +</P> +<P> +There are also three further options that can be set only at matching time: +</P> +<P> +<pre> + PCRE_NOTBOL +</PRE> +</P> +<P> +The first character of the 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. +</P> +<P> +<pre> + PCRE_NOTEOL +</PRE> +</P> +<P> +The end of the 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. +</P> +<P> +<pre> + PCRE_NOTEMPTY +</PRE> +</P> +<P> +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 +</P> +<P> +<pre> + a?b? +</PRE> +</P> +<P> +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> +<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 <b>split()</b> 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 set, and then if that fails by advancing the starting offset (see +below) and trying an ordinary match again. +</P> +<P> +The subject string is passed to <b>pcre_exec()</b> as a pointer in +<i>subject</i>, a length in <i>length</i>, and a starting offset in +<i>startoffset</i>. 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> +<P> +If the pattern was compiled with the PCRE_UTF8 option, the subject must be a +sequence of bytes that is a valid UTF-8 string. If an invalid UTF-8 string is +passed, PCRE's behaviour is not defined. +</P> +<P> +A non-zero starting offset is useful when searching for another match in the +same subject by calling <b>pcre_exec()</b> again after a previous success. +Setting <i>startoffset</i> 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 +</P> +<P> +<pre> + \Biss\B +</PRE> +</P> +<P> +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 <b>pcre_exec()</b> finds the first +occurrence. If <b>pcre_exec()</b> 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 +<b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i> +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> +<P> +If a non-zero starting offset is passed when the pattern is anchored, one +attempt to match at the given offset is tried. This can only succeed if the +pattern does not require the match to be at the start of the subject. +</P> +<P> +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> +<P> +Captured substrings are returned to the caller via a vector of integer offsets +whose address is passed in <i>ovector</i>. The number of elements in the vector +is passed in <i>ovecsize</i>. 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 <b>pcre_exec()</b> while +matching capturing subpatterns, and is not available for passing back +information. The length passed in <i>ovecsize</i> should always be a multiple of +three. If it is not, it is rounded down. +</P> +<P> +When a match has been successful, information about captured substrings is +returned in pairs of integers, starting at the beginning of <i>ovector</i>, and +continuing up to two-thirds of its length at the most. The first element of a +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. The +first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, 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 <b>pcre_exec()</b> +is the number of pairs that have been set. 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> +<P> +Some convenience functions are provided for extracting the captured substrings +as separate strings. These are described in the following section. +</P> +<P> +It is possible for an capturing subpattern number <i>n+1</i> to match some +part of the subject when subpattern <i>n</i> has not been used at all. For +example, if the string "abc" is matched against the pattern (a|(z))(bc) +subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset +values corresponding to the unused subpattern are set to -1. +</P> +<P> +If a capturing subpattern is matched repeatedly, it is the last portion of the +string that it matched that gets returned. +</P> +<P> +If the vector is too small to hold all the captured substrings, it is used as +far as possible (up to two-thirds of its length), and the function returns a +value of zero. In particular, if the substring offsets are not of interest, +<b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and +<i>ovecsize</i> as zero. However, if the pattern contains back references and +the <i>ovector</i> isn't 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 <i>ovector</i>. +</P> +<P> +Note that <b>pcre_info()</b> can be used to find out how many capturing +subpatterns there are in a compiled pattern. The smallest size for +<i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to +the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3. +</P> +<P> +If <b>pcre_exec()</b> fails, it returns a negative number. The following are +defined in the header file: +</P> +<P> +<pre> + PCRE_ERROR_NOMATCH (-1) +</PRE> +</P> +<P> +The subject string did not match the pattern. +</P> +<P> +<pre> + PCRE_ERROR_NULL (-2) +</PRE> +</P> +<P> +Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was +NULL and <i>ovecsize</i> was not zero. +</P> +<P> +<pre> + PCRE_ERROR_BADOPTION (-3) +</PRE> +</P> +<P> +An unrecognized bit was set in the <i>options</i> argument. +</P> +<P> +<pre> + PCRE_ERROR_BADMAGIC (-4) +</PRE> +</P> +<P> +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. This is the error it gives when the +magic number isn't present. +</P> +<P> +<pre> + PCRE_ERROR_UNKNOWN_NODE (-5) +</PRE> +</P> +<P> +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. +</P> +<P> +<pre> + PCRE_ERROR_NOMEMORY (-6) +</PRE> +</P> +<P> +If a pattern contains back references, but the <i>ovector</i> that is passed to +<b>pcre_exec()</b> 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 <b>pcre_malloc()</b> fails, this error is given. The memory is freed at +the end of matching. +</P> +<P> +<pre> + PCRE_ERROR_NOSUBSTRING (-7) +</PRE> +</P> +<P> +This error is used by the <b>pcre_copy_substring()</b>, +<b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see +below). It is never returned by <b>pcre_exec()</b>. +</P> +<P> +<pre> + PCRE_ERROR_MATCHLIMIT (-8) +</PRE> +</P> +<P> +The recursion and backtracking limit, as specified by the <i>match_limit</i> +field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the +description above. +</P> +<P> +<pre> + PCRE_ERROR_CALLOUT (-9) +</PRE> +</P> +<P> +This error is never generated by <b>pcre_exec()</b> itself. It is provided for +use by callout functions that want to yield a distinctive error code. See the +<b>pcrecallout</b> documentation for details. +</P> +<br><a name="SEC11" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br> +<P> +<b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b> +<b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b> +<b>int <i>buffersize</i>);</b> +</P> +<P> +<b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b> +<b>int <i>stringcount</i>, int <i>stringnumber</i>,</b> +<b>const char **<i>stringptr</i>);</b> +</P> +<P> +<b>int pcre_get_substring_list(const char *<i>subject</i>,</b> +<b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b> +</P> +<P> +Captured substrings can be accessed directly by using the offsets returned by +<b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions +<b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and +<b>pcre_get_substring_list()</b> 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. +</P> +<P> +The first three arguments are the same for all three of these functions: +<i>subject</i> is the subject string which has just been successfully matched, +<i>ovector</i> is a pointer to the vector of integer offsets that was passed to +<b>pcre_exec()</b>, and <i>stringcount</i> 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 <b>pcre_exec</b> if it is greater than +zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of space +in <i>ovector</i>, the value passed as <i>stringcount</i> should be the size of +the vector divided by three. +</P> +<P> +The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b> +extract a single substring, whose number is given as <i>stringnumber</i>. A +value of zero extracts the substring that matched the entire pattern, while +higher values extract the captured substrings. For <b>pcre_copy_substring()</b>, +the string is placed in <i>buffer</i>, whose length is given by +<i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is +obtained via <b>pcre_malloc</b>, and its address is returned via +<i>stringptr</i>. The yield of the function is the length of the string, not +including the terminating zero, or one of +</P> +<P> +<pre> + PCRE_ERROR_NOMEMORY (-6) +</PRE> +</P> +<P> +The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get +memory failed for <b>pcre_get_substring()</b>. +</P> +<P> +<pre> + PCRE_ERROR_NOSUBSTRING (-7) +</PRE> +</P> +<P> +There is no substring whose number is <i>stringnumber</i>. +</P> +<P> +The <b>pcre_get_substring_list()</b> function extracts all available substrings +and builds a list of pointers to them. All this is done in a single block of +memory which is obtained via <b>pcre_malloc</b>. The address of the memory block +is returned via <i>listptr</i>, 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 +</P> +<P> +<pre> + PCRE_ERROR_NOMEMORY (-6) +</PRE> +</P> +<P> +if the attempt to get the memory block failed. +</P> +<P> +When any of these functions encounter a substring that is unset, which can +happen when capturing subpattern number <i>n+1</i> matches some part of the +subject, but subpattern <i>n</i> 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 <i>ovector</i>, which is negative for unset +substrings. +</P> +<P> +The two convenience functions <b>pcre_free_substring()</b> and +<b>pcre_free_substring_list()</b> can be used to free the memory returned by +a previous call of <b>pcre_get_substring()</b> or +<b>pcre_get_substring_list()</b>, respectively. They do nothing more than call +the function pointed to by <b>pcre_free</b>, 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 which cannot use +<b>pcre_free</b> directly; it is for these cases that the functions are +provided. +</P> +<br><a name="SEC12" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br> +<P> +<b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b> +<b>const char *<i>subject</i>, int *<i>ovector</i>,</b> +<b>int <i>stringcount</i>, const char *<i>stringname</i>,</b> +<b>char *<i>buffer</i>, int <i>buffersize</i>);</b> +</P> +<P> +<b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b> +<b>const char *<i>name</i>);</b> +</P> +<P> +<b>int pcre_get_named_substring(const pcre *<i>code</i>,</b> +<b>const char *<i>subject</i>, int *<i>ovector</i>,</b> +<b>int <i>stringcount</i>, const char *<i>stringname</i>,</b> +<b>const char **<i>stringptr</i>);</b> +</P> +<P> +To extract a substring by name, you first have to find associated number. This +can be done by calling <b>pcre_get_stringnumber()</b>. The first argument is the +compiled pattern, and the second is the name. For example, for this pattern +</P> +<P> +<pre> + ab(?<xxx>\d+)... +</PRE> +</P> +<P> +the number of the subpattern called "xxx" is 1. Given the number, you can then +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> +<P> +Most of the arguments of <i>pcre_copy_named_substring()</i> and +<i>pcre_get_named_substring()</i> are the same as those for the functions that +extract by number, and so are not re-described here. There are just two +differences. +</P> +<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> +<P> +These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they +then call <i>pcre_copy_substring()</i> or <i>pcre_get_substring()</i>, as +appropriate. +</P> +<P> +Last updated: 03 February 2003 +<br> +Copyright © 1997-2003 University of Cambridge. |