+#include <pcre.h> +
+int (*pcre_callout)(pcre_callout_block *);
int (*pcre16_callout)(pcre16_callout_block *);
+int (*pcre32_callout)(pcre32_callout_block *); +
+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 pcre_callout (pcre16_callout for the 16-bit -library). By default, this variable contains NULL, which disables all calling -out. +library, pcre32_callout for the 32-bit library). By default, this +variable contains NULL, which disables all calling out.
Within a regular expression, (?C) indicates the points at which the external
@@ -56,20 +64,25 @@ it is processed as if it were
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:
+
+ (?(?C9)(?=a)ab|de) ++This applies only to assertion conditions (because they are themselves +independent groups). + +
+Automatic callouts can be used for tracking the progress of pattern matching. +The pcretest 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.
+-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. -
-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 @@ -93,12 +106,13 @@ option to the matching function, or by starting the pa (*NO_START_OPT). This slows down the matching process, but does ensure that callouts such as the example above are obeyed.
-During matching, when PCRE reaches a callout point, the external function -defined by pcre_callout or pcre16_callout 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 pcre_callout or pcre16_callout block. +defined by pcre_callout or pcre[16|32]_callout 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 pcre_callout +or pcre[16|32]_callout block. These structures contains the following fields:
int version; @@ -106,6 +120,7 @@ These structures contains the following fields: int *offset_vector; const char *subject; (8-bit version) PCRE_SPTR16 subject; (16-bit version) + PCRE_SPTR32 subject; (32-bit version) int subject_length; int start_match; int current_position; @@ -116,6 +131,7 @@ These structures contains the following fields: int next_item_length; const unsigned char *mark; (8-bit version) const PCRE_UCHAR16 *mark; (16-bit version) + const PCRE_UCHAR32 *mark; (32-bit version)The version field is an integer containing the version number of the block format. The initial version was 0; the current version is 2. The version @@ -130,10 +146,10 @@ automatically generated callouts).
The offset_vector field is a pointer to the vector of offsets that was passed by the caller to the matching function. When pcre_exec() or -pcre16_exec() 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. +pcre[16|32]_exec() 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.
The subject and subject_length fields contain copies of the values @@ -152,7 +168,7 @@ The current_position field contains the offset current match pointer.
-When the pcre_exec() or pcre16_exec() is used, the +When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top field contains one more than the number of the highest numbered captured substring so far. If no substrings have been captured, the value of capture_top is one. This is always the case when the DFA @@ -160,13 +176,15 @@ functions are used, because they do not support captur
The capture_last 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. +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 capture_last is -1. This is +always the case for the DFA matching functions.
The callout_data 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 callout_data field of a pcre_extra or pcre16_extra +in the callout_data field of a pcre_extra or pcre[16|32]_extra data structure. If no such data was passed, the value of callout_data in a callout block is NULL. There is a description of the pcre_extra structure in the @@ -192,13 +210,14 @@ same callout number. However, they are set for all cal
The mark field is present from version 2 of the callout structure. In -callouts from pcre_exec() or pcre16_exec() 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. +callouts from pcre_exec() or pcre[16|32]_exec() 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.
-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 @@ -212,7 +231,7 @@ values. In particular, PCRE_ERROR_NOMATCH forces a sta The error number PCRE_ERROR_CALLOUT is reserved for use by callout functions; it will never be used by PCRE itself.
-
Philip Hazel
@@ -221,11 +240,11 @@ University Computing Service
Cambridge CB2 3QH, England.
-Last updated: 08 Janurary 2012
+Last updated: 03 March 2013
-Copyright © 1997-2012 University of Cambridge.
+Copyright © 1997-2013 University of Cambridge.
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