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diff --git a/8.31/doc/html/pcrecallout.html b/8.31/doc/html/pcrecallout.html new file mode 100644 index 0000000..8076cee --- /dev/null +++ b/8.31/doc/html/pcrecallout.html @@ -0,0 +1,232 @@ +<html> +<head> +<title>pcrecallout specification</title> +</head> +<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> +<h1>pcrecallout man page</h1> +<p> +Return to the <a href="index.html">PCRE index page</a>. +</p> +<p> +This page is part of the PCRE HTML documentation. It was generated automatically +from the original man page. If there is any nonsense in it, please consult the +man page, in case the conversion went wrong. +<br> +<ul> +<li><a name="TOC1" href="#SEC1">PCRE CALLOUTS</a> +<li><a name="TOC2" href="#SEC2">MISSING CALLOUTS</a> +<li><a name="TOC3" href="#SEC3">THE CALLOUT INTERFACE</a> +<li><a name="TOC4" href="#SEC4">RETURN VALUES</a> +<li><a name="TOC5" href="#SEC5">AUTHOR</a> +<li><a name="TOC6" href="#SEC6">REVISION</a> +</ul> +<br><a name="SEC1" href="#TOC1">PCRE CALLOUTS</a><br> +<P> +<b>int (*pcre_callout)(pcre_callout_block *);</b> +</P> +<P> +<b>int (*pcre16_callout)(pcre16_callout_block *);</b> +</P> +<P> +PCRE provides a feature called "callout", which is a means of temporarily +passing control to the caller of PCRE in the middle of pattern matching. The +caller of PCRE provides an external function by putting its entry point in the +global variable <i>pcre_callout</i> (<i>pcre16_callout</i> for the 16-bit +library). By default, this variable contains NULL, which disables all calling +out. +</P> +<P> +Within a regular expression, (?C) indicates the points at which the external +function is to be called. Different callout points can be identified by putting +a number less than 256 after the letter C. The default value is zero. +For example, this pattern has two callout points: +<pre> + (?C1)abc(?C2)def +</pre> +If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, PCRE +automatically inserts callouts, all with number 255, before each item in the +pattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern +<pre> + A(\d{2}|--) +</pre> +it is processed as if it were +<br> +<br> +(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) +<br> +<br> +Notice that there is a callout before and after each parenthesis and +alternation bar. Automatic callouts can be used for tracking the progress of +pattern matching. The +<a href="pcretest.html"><b>pcretest</b></a> +command has an option that sets automatic callouts; when it is used, the output +indicates how the pattern is matched. This is useful information when you are +trying to optimize the performance of a particular pattern. +</P> +<P> +The use of callouts in a pattern makes it ineligible for optimization by the +just-in-time compiler. Studying such a pattern with the PCRE_STUDY_JIT_COMPILE +option always fails. +</P> +<br><a name="SEC2" href="#TOC1">MISSING CALLOUTS</a><br> +<P> +You should be aware that, because of optimizations in the way PCRE matches +patterns by default, callouts sometimes do not happen. For example, if the +pattern is +<pre> + ab(?C4)cd +</pre> +PCRE knows that any matching string must contain the letter "d". If the subject +string is "abyz", the lack of "d" means that matching doesn't ever start, and +the callout is never reached. However, with "abyd", though the result is still +no match, the callout is obeyed. +</P> +<P> +If the pattern is studied, PCRE knows the minimum length of a matching string, +and will immediately give a "no match" return without actually running a match +if the subject is not long enough, or, for unanchored patterns, if it has +been scanned far enough. +</P> +<P> +You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE +option to the matching function, or by starting the pattern with +(*NO_START_OPT). This slows down the matching process, but does ensure that +callouts such as the example above are obeyed. +</P> +<br><a name="SEC3" href="#TOC1">THE CALLOUT INTERFACE</a><br> +<P> +During matching, when PCRE reaches a callout point, the external function +defined by <i>pcre_callout</i> or <i>pcre16_callout</i> is called (if it is set). +This applies to both normal and DFA matching. The only argument to the callout +function is a pointer to a <b>pcre_callout</b> or <b>pcre16_callout</b> block. +These structures contains the following fields: +<pre> + int <i>version</i>; + int <i>callout_number</i>; + int *<i>offset_vector</i>; + const char *<i>subject</i>; (8-bit version) + PCRE_SPTR16 <i>subject</i>; (16-bit version) + int <i>subject_length</i>; + int <i>start_match</i>; + int <i>current_position</i>; + int <i>capture_top</i>; + int <i>capture_last</i>; + void *<i>callout_data</i>; + int <i>pattern_position</i>; + int <i>next_item_length</i>; + const unsigned char *<i>mark</i>; (8-bit version) + const PCRE_UCHAR16 *<i>mark</i>; (16-bit version) +</pre> +The <i>version</i> field is an integer containing the version number of the +block format. The initial version was 0; the current version is 2. The version +number will change again in future if additional fields are added, but the +intention is never to remove any of the existing fields. +</P> +<P> +The <i>callout_number</i> field contains the number of the callout, as compiled +into the pattern (that is, the number after ?C for manual callouts, and 255 for +automatically generated callouts). +</P> +<P> +The <i>offset_vector</i> field is a pointer to the vector of offsets that was +passed by the caller to the matching function. When <b>pcre_exec()</b> or +<b>pcre16_exec()</b> is used, the contents can be inspected, in order to extract +substrings that have been matched so far, in the same way as for extracting +substrings after a match has completed. For the DFA matching functions, this +field is not useful. +</P> +<P> +The <i>subject</i> and <i>subject_length</i> fields contain copies of the values +that were passed to the matching function. +</P> +<P> +The <i>start_match</i> field normally contains the offset within the subject at +which the current match attempt started. However, if the escape sequence \K +has been encountered, this value is changed to reflect the modified starting +point. If the pattern is not anchored, the callout function may be called +several times from the same point in the pattern for different starting points +in the subject. +</P> +<P> +The <i>current_position</i> field contains the offset within the subject of the +current match pointer. +</P> +<P> +When the <b>pcre_exec()</b> or <b>pcre16_exec()</b> is used, the +<i>capture_top</i> field contains one more than the number of the highest +numbered captured substring so far. If no substrings have been captured, the +value of <i>capture_top</i> is one. This is always the case when the DFA +functions are used, because they do not support captured substrings. +</P> +<P> +The <i>capture_last</i> field contains the number of the most recently captured +substring. If no substrings have been captured, its value is -1. This is always +the case for the DFA matching functions. +</P> +<P> +The <i>callout_data</i> field contains a value that is passed to a matching +function specifically so that it can be passed back in callouts. It is passed +in the <i>callout_data</i> field of a <b>pcre_extra</b> or <b>pcre16_extra</b> +data structure. If no such data was passed, the value of <i>callout_data</i> in +a callout block is NULL. There is a description of the <b>pcre_extra</b> +structure in the +<a href="pcreapi.html"><b>pcreapi</b></a> +documentation. +</P> +<P> +The <i>pattern_position</i> field is present from version 1 of the callout +structure. It contains the offset to the next item to be matched in the pattern +string. +</P> +<P> +The <i>next_item_length</i> field is present from version 1 of the callout +structure. It contains the length of the next item to be matched in the pattern +string. When the callout immediately precedes an alternation bar, a closing +parenthesis, or the end of the pattern, the length is zero. When the callout +precedes an opening parenthesis, the length is that of the entire subpattern. +</P> +<P> +The <i>pattern_position</i> and <i>next_item_length</i> fields are intended to +help in distinguishing between different automatic callouts, which all have the +same callout number. However, they are set for all callouts. +</P> +<P> +The <i>mark</i> field is present from version 2 of the callout structure. In +callouts from <b>pcre_exec()</b> or <b>pcre16_exec()</b> it contains a pointer to +the zero-terminated name of the most recently passed (*MARK), (*PRUNE), or +(*THEN) item in the match, or NULL if no such items have been passed. Instances +of (*PRUNE) or (*THEN) without a name do not obliterate a previous (*MARK). In +callouts from the DFA matching functions this field always contains NULL. +</P> +<br><a name="SEC4" href="#TOC1">RETURN VALUES</a><br> +<P> +The external callout function returns an integer to PCRE. If the value is zero, +matching proceeds as normal. If the value is greater than zero, matching fails +at the current point, but the testing of other matching possibilities goes +ahead, just as if a lookahead assertion had failed. If the value is less than +zero, the match is abandoned, the matching function returns the negative value. +</P> +<P> +Negative values should normally be chosen from the set of PCRE_ERROR_xxx +values. In particular, PCRE_ERROR_NOMATCH forces a standard "no match" failure. +The error number PCRE_ERROR_CALLOUT is reserved for use by callout functions; +it will never be used by PCRE itself. +</P> +<br><a name="SEC5" href="#TOC1">AUTHOR</a><br> +<P> +Philip Hazel +<br> +University Computing Service +<br> +Cambridge CB2 3QH, England. +<br> +</P> +<br><a name="SEC6" href="#TOC1">REVISION</a><br> +<P> +Last updated: 08 Janurary 2012 +<br> +Copyright © 1997-2012 University of Cambridge. +<br> +<p> +Return to the <a href="index.html">PCRE index page</a>. +</p> |