--- embedaddon/pcre/doc/pcrecallout.3 2012/02/21 23:05:52 1.1.1.1 +++ embedaddon/pcre/doc/pcrecallout.3 2014/06/15 19:46:05 1.1.1.5 @@ -1,16 +1,27 @@ -.TH PCRECALLOUT 3 +.TH PCRECALLOUT 3 "12 November 2013" "PCRE 8.34" .SH NAME PCRE - Perl-compatible regular expressions -.SH "PCRE CALLOUTS" +.SH SYNOPSIS .rs .sp +.B #include +.PP +.SM .B int (*pcre_callout)(pcre_callout_block *); .PP +.B int (*pcre16_callout)(pcre16_callout_block *); +.PP +.B int (*pcre32_callout)(pcre32_callout_block *); +. +.SH DESCRIPTION +.rs +.sp 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 \fIpcre_callout\fP. By default, this variable contains NULL, -which disables all calling out. +global variable \fIpcre_callout\fP (\fIpcre16_callout\fP for the 16-bit +library, \fIpcre32_callout\fP for the 32-bit library). By default, this +variable contains NULL, which disables all calling out. .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 @@ -19,10 +30,9 @@ For example, this pattern has two callout points: .sp (?C1)abc(?C2)def .sp -If the PCRE_AUTO_CALLOUT option bit is set when \fBpcre_compile()\fP or -\fBpcre_compile2()\fP is called, 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 +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 .sp A(\ed{2}|--) .sp @@ -31,27 +41,65 @@ it is processed as if it were (?C255)A(?C255)((?C255)\ed{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) .sp 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 +alternation bar. If the pattern contains a conditional group whose condition is +an assertion, an automatic callout is inserted immediately before the +condition. Such a callout may also be inserted explicitly, for example: +.sp + (?(?C9)(?=a)ab|de) +.sp +This applies only to assertion conditions (because they are themselves +independent groups). +.P +Automatic callouts can be used for tracking the progress of pattern matching. +The .\" HREF \fBpcretest\fP .\" -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 -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. +program has a pattern qualifier (/C) that sets automatic callouts; when it is +used, the output indicates how the pattern is being matched. This is useful +information when you are trying to optimize the performance of a particular +pattern. . . .SH "MISSING CALLOUTS" .rs .sp -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 +You should be aware that, because of optimizations in the way PCRE compiles and +matches patterns, callouts sometimes do not happen exactly as you might expect. +.P +At compile time, PCRE "auto-possessifies" repeated items when it knows that +what follows cannot be part of the repeat. For example, a+[bc] is compiled as +if it were a++[bc]. The \fBpcretest\fP output when this pattern is anchored and +then applied with automatic callouts to the string "aaaa" is: .sp + --->aaaa + +0 ^ ^ + +1 ^ a+ + +3 ^ ^ [bc] + No match +.sp +This indicates that when matching [bc] fails, there is no backtracking into a+ +and therefore the callouts that would be taken for the backtracks do not occur. +You can disable the auto-possessify feature by passing PCRE_NO_AUTO_POSSESS +to \fBpcre_compile()\fP, or starting the pattern with (*NO_AUTO_POSSESS). If +this is done in \fBpcretest\fP (using the /O qualifier), the output changes to +this: +.sp + --->aaaa + +0 ^ ^ + +1 ^ a+ + +3 ^ ^ [bc] + +3 ^ ^ [bc] + +3 ^ ^ [bc] + +3 ^^ [bc] + No match +.sp +This time, when matching [bc] fails, the matcher backtracks into a+ and tries +again, repeatedly, until a+ itself fails. +.P +Other optimizations that provide fast "no match" results also affect callouts. +For example, if the pattern is +.sp ab(?C4)cd .sp PCRE knows that any matching string must contain the letter "d". If the subject @@ -65,33 +113,38 @@ if the subject is not long enough, or, for unanchored been scanned far enough. .P You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE -option to \fBpcre_compile()\fP, \fBpcre_exec()\fP, or \fBpcre_dfa_exec()\fP, -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. +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. . . .SH "THE CALLOUT INTERFACE" .rs .sp During matching, when PCRE reaches a callout point, the external function -defined by \fIpcre_callout\fP is called (if it is set). This applies to both -the \fBpcre_exec()\fP and the \fBpcre_dfa_exec()\fP matching functions. The -only argument to the callout function is a pointer to a \fBpcre_callout\fP -block. This structure contains the following fields: +defined by \fIpcre_callout\fP or \fIpcre[16|32]_callout\fP 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 \fBpcre_callout\fP or +\fBpcre[16|32]_callout\fP block. These structures contains the following +fields: .sp - int \fIversion\fP; - int \fIcallout_number\fP; - int *\fIoffset_vector\fP; - const char *\fIsubject\fP; - int \fIsubject_length\fP; - int \fIstart_match\fP; - int \fIcurrent_position\fP; - int \fIcapture_top\fP; - int \fIcapture_last\fP; - void *\fIcallout_data\fP; - int \fIpattern_position\fP; - int \fInext_item_length\fP; - const unsigned char *\fImark\fP; + int \fIversion\fP; + int \fIcallout_number\fP; + int *\fIoffset_vector\fP; + const char *\fIsubject\fP; (8-bit version) + PCRE_SPTR16 \fIsubject\fP; (16-bit version) + PCRE_SPTR32 \fIsubject\fP; (32-bit version) + int \fIsubject_length\fP; + int \fIstart_match\fP; + int \fIcurrent_position\fP; + int \fIcapture_top\fP; + int \fIcapture_last\fP; + void *\fIcallout_data\fP; + int \fIpattern_position\fP; + int \fInext_item_length\fP; + const unsigned char *\fImark\fP; (8-bit version) + const PCRE_UCHAR16 *\fImark\fP; (16-bit version) + const PCRE_UCHAR32 *\fImark\fP; (32-bit version) .sp The \fIversion\fP field is an integer containing the version number of the block format. The initial version was 0; the current version is 2. The version @@ -103,14 +156,14 @@ into the pattern (that is, the number after ?C for man automatically generated callouts). .P The \fIoffset_vector\fP field is a pointer to the vector of offsets that was -passed by the caller to \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. When -\fBpcre_exec()\fP 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 \fBpcre_dfa_exec()\fP this field is -not useful. +passed by the caller to the matching function. When \fBpcre_exec()\fP or +\fBpcre[16|32]_exec()\fP 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 The \fIsubject\fP and \fIsubject_length\fP fields contain copies of the values -that were passed to \fBpcre_exec()\fP. +that were passed to the matching function. .P The \fIstart_match\fP field normally contains the offset within the subject at which the current match attempt started. However, if the escape sequence \eK @@ -122,48 +175,50 @@ in the subject. The \fIcurrent_position\fP field contains the offset within the subject of the current match pointer. .P -When the \fBpcre_exec()\fP function is used, the \fIcapture_top\fP field -contains one more than the number of the highest numbered captured substring so -far. If no substrings have been captured, the value of \fIcapture_top\fP is -one. This is always the case when \fBpcre_dfa_exec()\fP is used, because it -does not support captured substrings. +When the \fBpcre_exec()\fP or \fBpcre[16|32]_exec()\fP is used, the +\fIcapture_top\fP field contains one more than the number of the highest +numbered captured substring so far. If no substrings have been captured, the +value of \fIcapture_top\fP is one. This is always the case when the DFA +functions are used, because they do not support captured substrings. .P The \fIcapture_last\fP 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 when \fBpcre_dfa_exec()\fP is used. +substring. However, when a recursion exits, the value reverts to what it was +outside the recursion, as do the values of all captured substrings. If no +substrings have been captured, the value of \fIcapture_last\fP is -1. This is +always the case for the DFA matching functions. .P -The \fIcallout_data\fP field contains a value that is passed to -\fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP specifically so that it can be -passed back in callouts. It is passed in the \fIpcre_callout\fP field of the -\fBpcre_extra\fP data structure. If no such data was passed, the value of -\fIcallout_data\fP in a \fBpcre_callout\fP block is NULL. There is a -description of the \fBpcre_extra\fP structure in the +The \fIcallout_data\fP 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 \fIcallout_data\fP field of a \fBpcre_extra\fP or \fBpcre[16|32]_extra\fP +data structure. If no such data was passed, the value of \fIcallout_data\fP in +a callout block is NULL. There is a description of the \fBpcre_extra\fP +structure in the .\" HREF \fBpcreapi\fP .\" documentation. .P -The \fIpattern_position\fP field is present from version 1 of the -\fIpcre_callout\fP structure. It contains the offset to the next item to be -matched in the pattern string. +The \fIpattern_position\fP 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 -The \fInext_item_length\fP field is present from version 1 of the -\fIpcre_callout\fP 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. +The \fInext_item_length\fP 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 The \fIpattern_position\fP and \fInext_item_length\fP 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 -The \fImark\fP field is present from version 2 of the \fIpcre_callout\fP -structure. In callouts from \fBpcre_exec()\fP 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 \fBpcre_dfa_exec()\fP this field always contains NULL. +The \fImark\fP field is present from version 2 of the callout structure. In +callouts from \fBpcre_exec()\fP or \fBpcre[16|32]_exec()\fP 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. . . .SH "RETURN VALUES" @@ -173,8 +228,7 @@ The external callout function returns an integer to PC 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, and \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP -returns the negative value. +zero, the match is abandoned, the matching function returns the negative value. .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. @@ -196,6 +250,6 @@ Cambridge CB2 3QH, England. .rs .sp .nf -Last updated: 30 November 2011 -Copyright (c) 1997-2011 University of Cambridge. +Last updated: 12 November 2013 +Copyright (c) 1997-2013 University of Cambridge. .fi