1*22dc650dSSadaf Ebrahimi<html> 2*22dc650dSSadaf Ebrahimi<head> 3*22dc650dSSadaf Ebrahimi<title>pcre2callout specification</title> 4*22dc650dSSadaf Ebrahimi</head> 5*22dc650dSSadaf Ebrahimi<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> 6*22dc650dSSadaf Ebrahimi<h1>pcre2callout man page</h1> 7*22dc650dSSadaf Ebrahimi<p> 8*22dc650dSSadaf EbrahimiReturn to the <a href="index.html">PCRE2 index page</a>. 9*22dc650dSSadaf Ebrahimi</p> 10*22dc650dSSadaf Ebrahimi<p> 11*22dc650dSSadaf EbrahimiThis page is part of the PCRE2 HTML documentation. It was generated 12*22dc650dSSadaf Ebrahimiautomatically from the original man page. If there is any nonsense in it, 13*22dc650dSSadaf Ebrahimiplease consult the man page, in case the conversion went wrong. 14*22dc650dSSadaf Ebrahimi<br> 15*22dc650dSSadaf Ebrahimi<ul> 16*22dc650dSSadaf Ebrahimi<li><a name="TOC1" href="#SEC1">SYNOPSIS</a> 17*22dc650dSSadaf Ebrahimi<li><a name="TOC2" href="#SEC2">DESCRIPTION</a> 18*22dc650dSSadaf Ebrahimi<li><a name="TOC3" href="#SEC3">MISSING CALLOUTS</a> 19*22dc650dSSadaf Ebrahimi<li><a name="TOC4" href="#SEC4">THE CALLOUT INTERFACE</a> 20*22dc650dSSadaf Ebrahimi<li><a name="TOC5" href="#SEC5">RETURN VALUES FROM CALLOUTS</a> 21*22dc650dSSadaf Ebrahimi<li><a name="TOC6" href="#SEC6">CALLOUT ENUMERATION</a> 22*22dc650dSSadaf Ebrahimi<li><a name="TOC7" href="#SEC7">AUTHOR</a> 23*22dc650dSSadaf Ebrahimi<li><a name="TOC8" href="#SEC8">REVISION</a> 24*22dc650dSSadaf Ebrahimi</ul> 25*22dc650dSSadaf Ebrahimi<br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br> 26*22dc650dSSadaf Ebrahimi<P> 27*22dc650dSSadaf Ebrahimi<b>#include <pcre2.h></b> 28*22dc650dSSadaf Ebrahimi</P> 29*22dc650dSSadaf Ebrahimi<P> 30*22dc650dSSadaf Ebrahimi<b>int (*pcre2_callout)(pcre2_callout_block *, void *);</b> 31*22dc650dSSadaf Ebrahimi<br> 32*22dc650dSSadaf Ebrahimi<br> 33*22dc650dSSadaf Ebrahimi<b>int pcre2_callout_enumerate(const pcre2_code *<i>code</i>,</b> 34*22dc650dSSadaf Ebrahimi<b> int (*<i>callback</i>)(pcre2_callout_enumerate_block *, void *),</b> 35*22dc650dSSadaf Ebrahimi<b> void *<i>user_data</i>);</b> 36*22dc650dSSadaf Ebrahimi</P> 37*22dc650dSSadaf Ebrahimi<br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br> 38*22dc650dSSadaf Ebrahimi<P> 39*22dc650dSSadaf EbrahimiPCRE2 provides a feature called "callout", which is a means of temporarily 40*22dc650dSSadaf Ebrahimipassing control to the caller of PCRE2 in the middle of pattern matching. The 41*22dc650dSSadaf Ebrahimicaller of PCRE2 provides an external function by putting its entry point in 42*22dc650dSSadaf Ebrahimia match context (see <b>pcre2_set_callout()</b> in the 43*22dc650dSSadaf Ebrahimi<a href="pcre2api.html"><b>pcre2api</b></a> 44*22dc650dSSadaf Ebrahimidocumentation). 45*22dc650dSSadaf Ebrahimi</P> 46*22dc650dSSadaf Ebrahimi<P> 47*22dc650dSSadaf EbrahimiWhen using the <b>pcre2_substitute()</b> function, an additional callout feature 48*22dc650dSSadaf Ebrahimiis available. This does a callout after each change to the subject string and 49*22dc650dSSadaf Ebrahimiis described in the 50*22dc650dSSadaf Ebrahimi<a href="pcre2api.html"><b>pcre2api</b></a> 51*22dc650dSSadaf Ebrahimidocumentation; the rest of this document is concerned with callouts during 52*22dc650dSSadaf Ebrahimipattern matching. 53*22dc650dSSadaf Ebrahimi</P> 54*22dc650dSSadaf Ebrahimi<P> 55*22dc650dSSadaf EbrahimiWithin a regular expression, (?C<arg>) indicates a point at which the external 56*22dc650dSSadaf Ebrahimifunction is to be called. Different callout points can be identified by putting 57*22dc650dSSadaf Ebrahimia number less than 256 after the letter C. The default value is zero. 58*22dc650dSSadaf EbrahimiAlternatively, the argument may be a delimited string. The starting delimiter 59*22dc650dSSadaf Ebrahimimust be one of ` ' " ^ % # $ { and the ending delimiter is the same as the 60*22dc650dSSadaf Ebrahimistart, except for {, where the ending delimiter is }. If the ending delimiter 61*22dc650dSSadaf Ebrahimiis needed within the string, it must be doubled. For example, this pattern has 62*22dc650dSSadaf Ebrahimitwo callout points: 63*22dc650dSSadaf Ebrahimi<pre> 64*22dc650dSSadaf Ebrahimi (?C1)abc(?C"some ""arbitrary"" text")def 65*22dc650dSSadaf Ebrahimi</pre> 66*22dc650dSSadaf EbrahimiIf the PCRE2_AUTO_CALLOUT option bit is set when a pattern is compiled, PCRE2 67*22dc650dSSadaf Ebrahimiautomatically inserts callouts, all with number 255, before each item in the 68*22dc650dSSadaf Ebrahimipattern except for immediately before or after an explicit callout. For 69*22dc650dSSadaf Ebrahimiexample, if PCRE2_AUTO_CALLOUT is used with the pattern 70*22dc650dSSadaf Ebrahimi<pre> 71*22dc650dSSadaf Ebrahimi A(?C3)B 72*22dc650dSSadaf Ebrahimi</pre> 73*22dc650dSSadaf Ebrahimiit is processed as if it were 74*22dc650dSSadaf Ebrahimi<pre> 75*22dc650dSSadaf Ebrahimi (?C255)A(?C3)B(?C255) 76*22dc650dSSadaf Ebrahimi</pre> 77*22dc650dSSadaf EbrahimiHere is a more complicated example: 78*22dc650dSSadaf Ebrahimi<pre> 79*22dc650dSSadaf Ebrahimi A(\d{2}|--) 80*22dc650dSSadaf Ebrahimi</pre> 81*22dc650dSSadaf EbrahimiWith PCRE2_AUTO_CALLOUT, this pattern is processed as if it were 82*22dc650dSSadaf Ebrahimi<pre> 83*22dc650dSSadaf Ebrahimi (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) 84*22dc650dSSadaf Ebrahimi</pre> 85*22dc650dSSadaf EbrahimiNotice that there is a callout before and after each parenthesis and 86*22dc650dSSadaf Ebrahimialternation bar. If the pattern contains a conditional group whose condition is 87*22dc650dSSadaf Ebrahimian assertion, an automatic callout is inserted immediately before the 88*22dc650dSSadaf Ebrahimicondition. Such a callout may also be inserted explicitly, for example: 89*22dc650dSSadaf Ebrahimi<pre> 90*22dc650dSSadaf Ebrahimi (?(?C9)(?=a)ab|de) (?(?C%text%)(?!=d)ab|de) 91*22dc650dSSadaf Ebrahimi</pre> 92*22dc650dSSadaf EbrahimiThis applies only to assertion conditions (because they are themselves 93*22dc650dSSadaf Ebrahimiindependent groups). 94*22dc650dSSadaf Ebrahimi</P> 95*22dc650dSSadaf Ebrahimi<P> 96*22dc650dSSadaf EbrahimiCallouts can be useful for tracking the progress of pattern matching. The 97*22dc650dSSadaf Ebrahimi<a href="pcre2test.html"><b>pcre2test</b></a> 98*22dc650dSSadaf Ebrahimiprogram has a pattern qualifier (/auto_callout) that sets automatic callouts. 99*22dc650dSSadaf EbrahimiWhen any callouts are present, the output from <b>pcre2test</b> indicates how 100*22dc650dSSadaf Ebrahimithe pattern is being matched. This is useful information when you are trying to 101*22dc650dSSadaf Ebrahimioptimize the performance of a particular pattern. 102*22dc650dSSadaf Ebrahimi</P> 103*22dc650dSSadaf Ebrahimi<br><a name="SEC3" href="#TOC1">MISSING CALLOUTS</a><br> 104*22dc650dSSadaf Ebrahimi<P> 105*22dc650dSSadaf EbrahimiYou should be aware that, because of optimizations in the way PCRE2 compiles 106*22dc650dSSadaf Ebrahimiand matches patterns, callouts sometimes do not happen exactly as you might 107*22dc650dSSadaf Ebrahimiexpect. 108*22dc650dSSadaf Ebrahimi</P> 109*22dc650dSSadaf Ebrahimi<br><b> 110*22dc650dSSadaf EbrahimiAuto-possessification 111*22dc650dSSadaf Ebrahimi</b><br> 112*22dc650dSSadaf Ebrahimi<P> 113*22dc650dSSadaf EbrahimiAt compile time, PCRE2 "auto-possessifies" repeated items when it knows that 114*22dc650dSSadaf Ebrahimiwhat follows cannot be part of the repeat. For example, a+[bc] is compiled as 115*22dc650dSSadaf Ebrahimiif it were a++[bc]. The <b>pcre2test</b> output when this pattern is compiled 116*22dc650dSSadaf Ebrahimiwith PCRE2_ANCHORED and PCRE2_AUTO_CALLOUT and then applied to the string 117*22dc650dSSadaf Ebrahimi"aaaa" is: 118*22dc650dSSadaf Ebrahimi<pre> 119*22dc650dSSadaf Ebrahimi --->aaaa 120*22dc650dSSadaf Ebrahimi +0 ^ a+ 121*22dc650dSSadaf Ebrahimi +2 ^ ^ [bc] 122*22dc650dSSadaf Ebrahimi No match 123*22dc650dSSadaf Ebrahimi</pre> 124*22dc650dSSadaf EbrahimiThis indicates that when matching [bc] fails, there is no backtracking into a+ 125*22dc650dSSadaf Ebrahimi(because it is being treated as a++) and therefore the callouts that would be 126*22dc650dSSadaf Ebrahimitaken for the backtracks do not occur. You can disable the auto-possessify 127*22dc650dSSadaf Ebrahimifeature by passing PCRE2_NO_AUTO_POSSESS to <b>pcre2_compile()</b>, or starting 128*22dc650dSSadaf Ebrahimithe pattern with (*NO_AUTO_POSSESS). In this case, the output changes to this: 129*22dc650dSSadaf Ebrahimi<pre> 130*22dc650dSSadaf Ebrahimi --->aaaa 131*22dc650dSSadaf Ebrahimi +0 ^ a+ 132*22dc650dSSadaf Ebrahimi +2 ^ ^ [bc] 133*22dc650dSSadaf Ebrahimi +2 ^ ^ [bc] 134*22dc650dSSadaf Ebrahimi +2 ^ ^ [bc] 135*22dc650dSSadaf Ebrahimi +2 ^^ [bc] 136*22dc650dSSadaf Ebrahimi No match 137*22dc650dSSadaf Ebrahimi</pre> 138*22dc650dSSadaf EbrahimiThis time, when matching [bc] fails, the matcher backtracks into a+ and tries 139*22dc650dSSadaf Ebrahimiagain, repeatedly, until a+ itself fails. 140*22dc650dSSadaf Ebrahimi</P> 141*22dc650dSSadaf Ebrahimi<br><b> 142*22dc650dSSadaf EbrahimiAutomatic .* anchoring 143*22dc650dSSadaf Ebrahimi</b><br> 144*22dc650dSSadaf Ebrahimi<P> 145*22dc650dSSadaf EbrahimiBy default, an optimization is applied when .* is the first significant item in 146*22dc650dSSadaf Ebrahimia pattern. If PCRE2_DOTALL is set, so that the dot can match any character, the 147*22dc650dSSadaf Ebrahimipattern is automatically anchored. If PCRE2_DOTALL is not set, a match can 148*22dc650dSSadaf Ebrahimistart only after an internal newline or at the beginning of the subject, and 149*22dc650dSSadaf Ebrahimi<b>pcre2_compile()</b> remembers this. If a pattern has more than one top-level 150*22dc650dSSadaf Ebrahimibranch, automatic anchoring occurs if all branches are anchorable. 151*22dc650dSSadaf Ebrahimi</P> 152*22dc650dSSadaf Ebrahimi<P> 153*22dc650dSSadaf EbrahimiThis optimization is disabled, however, if .* is in an atomic group or if there 154*22dc650dSSadaf Ebrahimiis a backreference to the capture group in which it appears. It is also 155*22dc650dSSadaf Ebrahimidisabled if the pattern contains (*PRUNE) or (*SKIP). However, the presence of 156*22dc650dSSadaf Ebrahimicallouts does not affect it. 157*22dc650dSSadaf Ebrahimi</P> 158*22dc650dSSadaf Ebrahimi<P> 159*22dc650dSSadaf EbrahimiFor example, if the pattern .*\d is compiled with PCRE2_AUTO_CALLOUT and 160*22dc650dSSadaf Ebrahimiapplied to the string "aa", the <b>pcre2test</b> output is: 161*22dc650dSSadaf Ebrahimi<pre> 162*22dc650dSSadaf Ebrahimi --->aa 163*22dc650dSSadaf Ebrahimi +0 ^ .* 164*22dc650dSSadaf Ebrahimi +2 ^ ^ \d 165*22dc650dSSadaf Ebrahimi +2 ^^ \d 166*22dc650dSSadaf Ebrahimi +2 ^ \d 167*22dc650dSSadaf Ebrahimi No match 168*22dc650dSSadaf Ebrahimi</pre> 169*22dc650dSSadaf EbrahimiThis shows that all match attempts start at the beginning of the subject. In 170*22dc650dSSadaf Ebrahimiother words, the pattern is anchored. You can disable this optimization by 171*22dc650dSSadaf Ebrahimipassing PCRE2_NO_DOTSTAR_ANCHOR to <b>pcre2_compile()</b>, or starting the 172*22dc650dSSadaf Ebrahimipattern with (*NO_DOTSTAR_ANCHOR). In this case, the output changes to: 173*22dc650dSSadaf Ebrahimi<pre> 174*22dc650dSSadaf Ebrahimi --->aa 175*22dc650dSSadaf Ebrahimi +0 ^ .* 176*22dc650dSSadaf Ebrahimi +2 ^ ^ \d 177*22dc650dSSadaf Ebrahimi +2 ^^ \d 178*22dc650dSSadaf Ebrahimi +2 ^ \d 179*22dc650dSSadaf Ebrahimi +0 ^ .* 180*22dc650dSSadaf Ebrahimi +2 ^^ \d 181*22dc650dSSadaf Ebrahimi +2 ^ \d 182*22dc650dSSadaf Ebrahimi No match 183*22dc650dSSadaf Ebrahimi</pre> 184*22dc650dSSadaf EbrahimiThis shows more match attempts, starting at the second subject character. 185*22dc650dSSadaf EbrahimiAnother optimization, described in the next section, means that there is no 186*22dc650dSSadaf Ebrahimisubsequent attempt to match with an empty subject. 187*22dc650dSSadaf Ebrahimi</P> 188*22dc650dSSadaf Ebrahimi<br><b> 189*22dc650dSSadaf EbrahimiOther optimizations 190*22dc650dSSadaf Ebrahimi</b><br> 191*22dc650dSSadaf Ebrahimi<P> 192*22dc650dSSadaf EbrahimiOther optimizations that provide fast "no match" results also affect callouts. 193*22dc650dSSadaf EbrahimiFor example, if the pattern is 194*22dc650dSSadaf Ebrahimi<pre> 195*22dc650dSSadaf Ebrahimi ab(?C4)cd 196*22dc650dSSadaf Ebrahimi</pre> 197*22dc650dSSadaf EbrahimiPCRE2 knows that any matching string must contain the letter "d". If the 198*22dc650dSSadaf Ebrahimisubject string is "abyz", the lack of "d" means that matching doesn't ever 199*22dc650dSSadaf Ebrahimistart, and the callout is never reached. However, with "abyd", though the 200*22dc650dSSadaf Ebrahimiresult is still no match, the callout is obeyed. 201*22dc650dSSadaf Ebrahimi</P> 202*22dc650dSSadaf Ebrahimi<P> 203*22dc650dSSadaf EbrahimiFor most patterns PCRE2 also knows the minimum length of a matching string, and 204*22dc650dSSadaf Ebrahimiwill immediately give a "no match" return without actually running a match if 205*22dc650dSSadaf Ebrahimithe subject is not long enough, or, for unanchored patterns, if it has been 206*22dc650dSSadaf Ebrahimiscanned far enough. 207*22dc650dSSadaf Ebrahimi</P> 208*22dc650dSSadaf Ebrahimi<P> 209*22dc650dSSadaf EbrahimiYou can disable these optimizations by passing the PCRE2_NO_START_OPTIMIZE 210*22dc650dSSadaf Ebrahimioption to <b>pcre2_compile()</b>, or by starting the pattern with 211*22dc650dSSadaf Ebrahimi(*NO_START_OPT). This slows down the matching process, but does ensure that 212*22dc650dSSadaf Ebrahimicallouts such as the example above are obeyed. 213*22dc650dSSadaf Ebrahimi<a name="calloutinterface"></a></P> 214*22dc650dSSadaf Ebrahimi<br><a name="SEC4" href="#TOC1">THE CALLOUT INTERFACE</a><br> 215*22dc650dSSadaf Ebrahimi<P> 216*22dc650dSSadaf EbrahimiDuring matching, when PCRE2 reaches a callout point, if an external function is 217*22dc650dSSadaf Ebrahimiprovided in the match context, it is called. This applies to both normal, 218*22dc650dSSadaf EbrahimiDFA, and JIT matching. The first argument to the callout function is a pointer 219*22dc650dSSadaf Ebrahimito a <b>pcre2_callout</b> block. The second argument is the void * callout data 220*22dc650dSSadaf Ebrahimithat was supplied when the callout was set up by calling 221*22dc650dSSadaf Ebrahimi<b>pcre2_set_callout()</b> (see the 222*22dc650dSSadaf Ebrahimi<a href="pcre2api.html"><b>pcre2api</b></a> 223*22dc650dSSadaf Ebrahimidocumentation). The callout block structure contains the following fields, not 224*22dc650dSSadaf Ebrahiminecessarily in this order: 225*22dc650dSSadaf Ebrahimi<pre> 226*22dc650dSSadaf Ebrahimi uint32_t <i>version</i>; 227*22dc650dSSadaf Ebrahimi uint32_t <i>callout_number</i>; 228*22dc650dSSadaf Ebrahimi uint32_t <i>capture_top</i>; 229*22dc650dSSadaf Ebrahimi uint32_t <i>capture_last</i>; 230*22dc650dSSadaf Ebrahimi uint32_t <i>callout_flags</i>; 231*22dc650dSSadaf Ebrahimi PCRE2_SIZE *<i>offset_vector</i>; 232*22dc650dSSadaf Ebrahimi PCRE2_SPTR <i>mark</i>; 233*22dc650dSSadaf Ebrahimi PCRE2_SPTR <i>subject</i>; 234*22dc650dSSadaf Ebrahimi PCRE2_SIZE <i>subject_length</i>; 235*22dc650dSSadaf Ebrahimi PCRE2_SIZE <i>start_match</i>; 236*22dc650dSSadaf Ebrahimi PCRE2_SIZE <i>current_position</i>; 237*22dc650dSSadaf Ebrahimi PCRE2_SIZE <i>pattern_position</i>; 238*22dc650dSSadaf Ebrahimi PCRE2_SIZE <i>next_item_length</i>; 239*22dc650dSSadaf Ebrahimi PCRE2_SIZE <i>callout_string_offset</i>; 240*22dc650dSSadaf Ebrahimi PCRE2_SIZE <i>callout_string_length</i>; 241*22dc650dSSadaf Ebrahimi PCRE2_SPTR <i>callout_string</i>; 242*22dc650dSSadaf Ebrahimi</pre> 243*22dc650dSSadaf EbrahimiThe <i>version</i> field contains the version number of the block format. The 244*22dc650dSSadaf Ebrahimicurrent version is 2; the three callout string fields were added for version 1, 245*22dc650dSSadaf Ebrahimiand the <i>callout_flags</i> field for version 2. If you are writing an 246*22dc650dSSadaf Ebrahimiapplication that might use an earlier release of PCRE2, you should check the 247*22dc650dSSadaf Ebrahimiversion number before accessing any of these fields. The version number will 248*22dc650dSSadaf Ebrahimiincrease in future if more fields are added, but the intention is never to 249*22dc650dSSadaf Ebrahimiremove any of the existing fields. 250*22dc650dSSadaf Ebrahimi</P> 251*22dc650dSSadaf Ebrahimi<br><b> 252*22dc650dSSadaf EbrahimiFields for numerical callouts 253*22dc650dSSadaf Ebrahimi</b><br> 254*22dc650dSSadaf Ebrahimi<P> 255*22dc650dSSadaf EbrahimiFor a numerical callout, <i>callout_string</i> is NULL, and <i>callout_number</i> 256*22dc650dSSadaf Ebrahimicontains the number of the callout, in the range 0-255. This is the number 257*22dc650dSSadaf Ebrahimithat follows (?C for callouts that part of the pattern; it is 255 for 258*22dc650dSSadaf Ebrahimiautomatically generated callouts. 259*22dc650dSSadaf Ebrahimi</P> 260*22dc650dSSadaf Ebrahimi<br><b> 261*22dc650dSSadaf EbrahimiFields for string callouts 262*22dc650dSSadaf Ebrahimi</b><br> 263*22dc650dSSadaf Ebrahimi<P> 264*22dc650dSSadaf EbrahimiFor callouts with string arguments, <i>callout_number</i> is always zero, and 265*22dc650dSSadaf Ebrahimi<i>callout_string</i> points to the string that is contained within the compiled 266*22dc650dSSadaf Ebrahimipattern. Its length is given by <i>callout_string_length</i>. Duplicated ending 267*22dc650dSSadaf Ebrahimidelimiters that were present in the original pattern string have been turned 268*22dc650dSSadaf Ebrahimiinto single characters, but there is no other processing of the callout string 269*22dc650dSSadaf Ebrahimiargument. An additional code unit containing binary zero is present after the 270*22dc650dSSadaf Ebrahimistring, but is not included in the length. The delimiter that was used to start 271*22dc650dSSadaf Ebrahimithe string is also stored within the pattern, immediately before the string 272*22dc650dSSadaf Ebrahimiitself. You can access this delimiter as <i>callout_string</i>[-1] if you need 273*22dc650dSSadaf Ebrahimiit. 274*22dc650dSSadaf Ebrahimi</P> 275*22dc650dSSadaf Ebrahimi<P> 276*22dc650dSSadaf EbrahimiThe <i>callout_string_offset</i> field is the code unit offset to the start of 277*22dc650dSSadaf Ebrahimithe callout argument string within the original pattern string. This is 278*22dc650dSSadaf Ebrahimiprovided for the benefit of applications such as script languages that might 279*22dc650dSSadaf Ebrahimineed to report errors in the callout string within the pattern. 280*22dc650dSSadaf Ebrahimi</P> 281*22dc650dSSadaf Ebrahimi<br><b> 282*22dc650dSSadaf EbrahimiFields for all callouts 283*22dc650dSSadaf Ebrahimi</b><br> 284*22dc650dSSadaf Ebrahimi<P> 285*22dc650dSSadaf EbrahimiThe remaining fields in the callout block are the same for both kinds of 286*22dc650dSSadaf Ebrahimicallout. 287*22dc650dSSadaf Ebrahimi</P> 288*22dc650dSSadaf Ebrahimi<P> 289*22dc650dSSadaf EbrahimiThe <i>offset_vector</i> field is a pointer to a vector of capturing offsets 290*22dc650dSSadaf Ebrahimi(the "ovector"). You may read the elements in this vector, but you must not 291*22dc650dSSadaf Ebrahimichange any of them. 292*22dc650dSSadaf Ebrahimi</P> 293*22dc650dSSadaf Ebrahimi<P> 294*22dc650dSSadaf EbrahimiFor calls to <b>pcre2_match()</b>, the <i>offset_vector</i> field is not (since 295*22dc650dSSadaf Ebrahimirelease 10.30) a pointer to the actual ovector that was passed to the matching 296*22dc650dSSadaf Ebrahimifunction in the match data block. Instead it points to an internal ovector of a 297*22dc650dSSadaf Ebrahimisize large enough to hold all possible captured substrings in the pattern. Note 298*22dc650dSSadaf Ebrahimithat whenever a recursion or subroutine call within a pattern completes, the 299*22dc650dSSadaf Ebrahimicapturing state is reset to what it was before. 300*22dc650dSSadaf Ebrahimi</P> 301*22dc650dSSadaf Ebrahimi<P> 302*22dc650dSSadaf EbrahimiThe <i>capture_last</i> field contains the number of the most recently captured 303*22dc650dSSadaf Ebrahimisubstring, and the <i>capture_top</i> field contains one more than the number of 304*22dc650dSSadaf Ebrahimithe highest numbered captured substring so far. If no substrings have yet been 305*22dc650dSSadaf Ebrahimicaptured, the value of <i>capture_last</i> is 0 and the value of 306*22dc650dSSadaf Ebrahimi<i>capture_top</i> is 1. The values of these fields do not always differ by one; 307*22dc650dSSadaf Ebrahimifor example, when the callout in the pattern ((a)(b))(?C2) is taken, 308*22dc650dSSadaf Ebrahimi<i>capture_last</i> is 1 but <i>capture_top</i> is 4. 309*22dc650dSSadaf Ebrahimi</P> 310*22dc650dSSadaf Ebrahimi<P> 311*22dc650dSSadaf EbrahimiThe contents of ovector[2] to ovector[<capture_top>*2-1] can be inspected in 312*22dc650dSSadaf Ebrahimiorder to extract substrings that have been matched so far, in the same way as 313*22dc650dSSadaf Ebrahimiextracting substrings after a match has completed. The values in ovector[0] and 314*22dc650dSSadaf Ebrahimiovector[1] are always PCRE2_UNSET because the match is by definition not 315*22dc650dSSadaf Ebrahimicomplete. Substrings that have not been captured but whose numbers are less 316*22dc650dSSadaf Ebrahimithan <i>capture_top</i> also have both of their ovector slots set to 317*22dc650dSSadaf EbrahimiPCRE2_UNSET. 318*22dc650dSSadaf Ebrahimi</P> 319*22dc650dSSadaf Ebrahimi<P> 320*22dc650dSSadaf EbrahimiFor DFA matching, the <i>offset_vector</i> field points to the ovector that was 321*22dc650dSSadaf Ebrahimipassed to the matching function in the match data block for callouts at the top 322*22dc650dSSadaf Ebrahimilevel, but to an internal ovector during the processing of pattern recursions, 323*22dc650dSSadaf Ebrahimilookarounds, and atomic groups. However, these ovectors hold no useful 324*22dc650dSSadaf Ebrahimiinformation because <b>pcre2_dfa_match()</b> does not support substring 325*22dc650dSSadaf Ebrahimicapturing. The value of <i>capture_top</i> is always 1 and the value of 326*22dc650dSSadaf Ebrahimi<i>capture_last</i> is always 0 for DFA matching. 327*22dc650dSSadaf Ebrahimi</P> 328*22dc650dSSadaf Ebrahimi<P> 329*22dc650dSSadaf EbrahimiThe <i>subject</i> and <i>subject_length</i> fields contain copies of the values 330*22dc650dSSadaf Ebrahimithat were passed to the matching function. 331*22dc650dSSadaf Ebrahimi</P> 332*22dc650dSSadaf Ebrahimi<P> 333*22dc650dSSadaf EbrahimiThe <i>start_match</i> field normally contains the offset within the subject at 334*22dc650dSSadaf Ebrahimiwhich the current match attempt started. However, if the escape sequence \K 335*22dc650dSSadaf Ebrahimihas been encountered, this value is changed to reflect the modified starting 336*22dc650dSSadaf Ebrahimipoint. If the pattern is not anchored, the callout function may be called 337*22dc650dSSadaf Ebrahimiseveral times from the same point in the pattern for different starting points 338*22dc650dSSadaf Ebrahimiin the subject. 339*22dc650dSSadaf Ebrahimi</P> 340*22dc650dSSadaf Ebrahimi<P> 341*22dc650dSSadaf EbrahimiThe <i>current_position</i> field contains the offset within the subject of the 342*22dc650dSSadaf Ebrahimicurrent match pointer. 343*22dc650dSSadaf Ebrahimi</P> 344*22dc650dSSadaf Ebrahimi<P> 345*22dc650dSSadaf EbrahimiThe <i>pattern_position</i> field contains the offset in the pattern string to 346*22dc650dSSadaf Ebrahimithe next item to be matched. 347*22dc650dSSadaf Ebrahimi</P> 348*22dc650dSSadaf Ebrahimi<P> 349*22dc650dSSadaf EbrahimiThe <i>next_item_length</i> field contains the length of the next item to be 350*22dc650dSSadaf Ebrahimiprocessed in the pattern string. When the callout is at the end of the pattern, 351*22dc650dSSadaf Ebrahimithe length is zero. When the callout precedes an opening parenthesis, the 352*22dc650dSSadaf Ebrahimilength includes meta characters that follow the parenthesis. For example, in a 353*22dc650dSSadaf Ebrahimicallout before an assertion such as (?=ab) the length is 3. For an alternation 354*22dc650dSSadaf Ebrahimibar or a closing parenthesis, the length is one, unless a closing parenthesis 355*22dc650dSSadaf Ebrahimiis followed by a quantifier, in which case its length is included. (This 356*22dc650dSSadaf Ebrahimichanged in release 10.23. In earlier releases, before an opening parenthesis 357*22dc650dSSadaf Ebrahimithe length was that of the entire group, and before an alternation bar or a 358*22dc650dSSadaf Ebrahimiclosing parenthesis the length was zero.) 359*22dc650dSSadaf Ebrahimi</P> 360*22dc650dSSadaf Ebrahimi<P> 361*22dc650dSSadaf EbrahimiThe <i>pattern_position</i> and <i>next_item_length</i> fields are intended to 362*22dc650dSSadaf Ebrahimihelp in distinguishing between different automatic callouts, which all have the 363*22dc650dSSadaf Ebrahimisame callout number. However, they are set for all callouts, and are used by 364*22dc650dSSadaf Ebrahimi<b>pcre2test</b> to show the next item to be matched when displaying callout 365*22dc650dSSadaf Ebrahimiinformation. 366*22dc650dSSadaf Ebrahimi</P> 367*22dc650dSSadaf Ebrahimi<P> 368*22dc650dSSadaf EbrahimiIn callouts from <b>pcre2_match()</b> the <i>mark</i> field contains a pointer to 369*22dc650dSSadaf Ebrahimithe zero-terminated name of the most recently passed (*MARK), (*PRUNE), or 370*22dc650dSSadaf Ebrahimi(*THEN) item in the match, or NULL if no such items have been passed. Instances 371*22dc650dSSadaf Ebrahimiof (*PRUNE) or (*THEN) without a name do not obliterate a previous (*MARK). In 372*22dc650dSSadaf Ebrahimicallouts from the DFA matching function this field always contains NULL. 373*22dc650dSSadaf Ebrahimi</P> 374*22dc650dSSadaf Ebrahimi<P> 375*22dc650dSSadaf EbrahimiThe <i>callout_flags</i> field is always zero in callouts from 376*22dc650dSSadaf Ebrahimi<b>pcre2_dfa_match()</b> or when JIT is being used. When <b>pcre2_match()</b> 377*22dc650dSSadaf Ebrahimiwithout JIT is used, the following bits may be set: 378*22dc650dSSadaf Ebrahimi<pre> 379*22dc650dSSadaf Ebrahimi PCRE2_CALLOUT_STARTMATCH 380*22dc650dSSadaf Ebrahimi</pre> 381*22dc650dSSadaf EbrahimiThis is set for the first callout after the start of matching for each new 382*22dc650dSSadaf Ebrahimistarting position in the subject. 383*22dc650dSSadaf Ebrahimi<pre> 384*22dc650dSSadaf Ebrahimi PCRE2_CALLOUT_BACKTRACK 385*22dc650dSSadaf Ebrahimi</pre> 386*22dc650dSSadaf EbrahimiThis is set if there has been a matching backtrack since the previous callout, 387*22dc650dSSadaf Ebrahimior since the start of matching if this is the first callout from a 388*22dc650dSSadaf Ebrahimi<b>pcre2_match()</b> run. 389*22dc650dSSadaf Ebrahimi</P> 390*22dc650dSSadaf Ebrahimi<P> 391*22dc650dSSadaf EbrahimiBoth bits are set when a backtrack has caused a "bumpalong" to a new starting 392*22dc650dSSadaf Ebrahimiposition in the subject. Output from <b>pcre2test</b> does not indicate the 393*22dc650dSSadaf Ebrahimipresence of these bits unless the <b>callout_extra</b> modifier is set. 394*22dc650dSSadaf Ebrahimi</P> 395*22dc650dSSadaf Ebrahimi<P> 396*22dc650dSSadaf EbrahimiThe information in the <b>callout_flags</b> field is provided so that 397*22dc650dSSadaf Ebrahimiapplications can track and tell their users how matching with backtracking is 398*22dc650dSSadaf Ebrahimidone. This can be useful when trying to optimize patterns, or just to 399*22dc650dSSadaf Ebrahimiunderstand how PCRE2 works. There is no support in <b>pcre2_dfa_match()</b> 400*22dc650dSSadaf Ebrahimibecause there is no backtracking in DFA matching, and there is no support in 401*22dc650dSSadaf EbrahimiJIT because JIT is all about maximimizing matching performance. In both these 402*22dc650dSSadaf Ebrahimicases the <b>callout_flags</b> field is always zero. 403*22dc650dSSadaf Ebrahimi</P> 404*22dc650dSSadaf Ebrahimi<br><a name="SEC5" href="#TOC1">RETURN VALUES FROM CALLOUTS</a><br> 405*22dc650dSSadaf Ebrahimi<P> 406*22dc650dSSadaf EbrahimiThe external callout function returns an integer to PCRE2. If the value is 407*22dc650dSSadaf Ebrahimizero, matching proceeds as normal. If the value is greater than zero, matching 408*22dc650dSSadaf Ebrahimifails at the current point, but the testing of other matching possibilities 409*22dc650dSSadaf Ebrahimigoes ahead, just as if a lookahead assertion had failed. If the value is less 410*22dc650dSSadaf Ebrahimithan zero, the match is abandoned, and the matching function returns the 411*22dc650dSSadaf Ebrahiminegative value. 412*22dc650dSSadaf Ebrahimi</P> 413*22dc650dSSadaf Ebrahimi<P> 414*22dc650dSSadaf EbrahimiNegative values should normally be chosen from the set of PCRE2_ERROR_xxx 415*22dc650dSSadaf Ebrahimivalues. In particular, PCRE2_ERROR_NOMATCH forces a standard "no match" 416*22dc650dSSadaf Ebrahimifailure. The error number PCRE2_ERROR_CALLOUT is reserved for use by callout 417*22dc650dSSadaf Ebrahimifunctions; it will never be used by PCRE2 itself. 418*22dc650dSSadaf Ebrahimi</P> 419*22dc650dSSadaf Ebrahimi<br><a name="SEC6" href="#TOC1">CALLOUT ENUMERATION</a><br> 420*22dc650dSSadaf Ebrahimi<P> 421*22dc650dSSadaf Ebrahimi<b>int pcre2_callout_enumerate(const pcre2_code *<i>code</i>,</b> 422*22dc650dSSadaf Ebrahimi<b> int (*<i>callback</i>)(pcre2_callout_enumerate_block *, void *),</b> 423*22dc650dSSadaf Ebrahimi<b> void *<i>user_data</i>);</b> 424*22dc650dSSadaf Ebrahimi<br> 425*22dc650dSSadaf Ebrahimi<br> 426*22dc650dSSadaf EbrahimiA script language that supports the use of string arguments in callouts might 427*22dc650dSSadaf Ebrahimilike to scan all the callouts in a pattern before running the match. This can 428*22dc650dSSadaf Ebrahimibe done by calling <b>pcre2_callout_enumerate()</b>. The first argument is a 429*22dc650dSSadaf Ebrahimipointer to a compiled pattern, the second points to a callback function, and 430*22dc650dSSadaf Ebrahimithe third is arbitrary user data. The callback function is called for every 431*22dc650dSSadaf Ebrahimicallout in the pattern in the order in which they appear. Its first argument is 432*22dc650dSSadaf Ebrahimia pointer to a callout enumeration block, and its second argument is the 433*22dc650dSSadaf Ebrahimi<i>user_data</i> value that was passed to <b>pcre2_callout_enumerate()</b>. The 434*22dc650dSSadaf Ebrahimidata block contains the following fields: 435*22dc650dSSadaf Ebrahimi<pre> 436*22dc650dSSadaf Ebrahimi <i>version</i> Block version number 437*22dc650dSSadaf Ebrahimi <i>pattern_position</i> Offset to next item in pattern 438*22dc650dSSadaf Ebrahimi <i>next_item_length</i> Length of next item in pattern 439*22dc650dSSadaf Ebrahimi <i>callout_number</i> Number for numbered callouts 440*22dc650dSSadaf Ebrahimi <i>callout_string_offset</i> Offset to string within pattern 441*22dc650dSSadaf Ebrahimi <i>callout_string_length</i> Length of callout string 442*22dc650dSSadaf Ebrahimi <i>callout_string</i> Points to callout string or is NULL 443*22dc650dSSadaf Ebrahimi</pre> 444*22dc650dSSadaf EbrahimiThe version number is currently 0. It will increase if new fields are ever 445*22dc650dSSadaf Ebrahimiadded to the block. The remaining fields are the same as their namesakes in the 446*22dc650dSSadaf Ebrahimi<b>pcre2_callout</b> block that is used for callouts during matching, as 447*22dc650dSSadaf Ebrahimidescribed 448*22dc650dSSadaf Ebrahimi<a href="#calloutinterface">above.</a> 449*22dc650dSSadaf Ebrahimi</P> 450*22dc650dSSadaf Ebrahimi<P> 451*22dc650dSSadaf EbrahimiNote that the value of <i>pattern_position</i> is unique for each callout. 452*22dc650dSSadaf EbrahimiHowever, if a callout occurs inside a group that is quantified with a non-zero 453*22dc650dSSadaf Ebrahimiminimum or a fixed maximum, the group is replicated inside the compiled 454*22dc650dSSadaf Ebrahimipattern. For example, a pattern such as /(a){2}/ is compiled as if it were 455*22dc650dSSadaf Ebrahimi/(a)(a)/. This means that the callout will be enumerated more than once, but 456*22dc650dSSadaf Ebrahimiwith the same value for <i>pattern_position</i> in each case. 457*22dc650dSSadaf Ebrahimi</P> 458*22dc650dSSadaf Ebrahimi<P> 459*22dc650dSSadaf EbrahimiThe callback function should normally return zero. If it returns a non-zero 460*22dc650dSSadaf Ebrahimivalue, scanning the pattern stops, and that value is returned from 461*22dc650dSSadaf Ebrahimi<b>pcre2_callout_enumerate()</b>. 462*22dc650dSSadaf Ebrahimi</P> 463*22dc650dSSadaf Ebrahimi<br><a name="SEC7" href="#TOC1">AUTHOR</a><br> 464*22dc650dSSadaf Ebrahimi<P> 465*22dc650dSSadaf EbrahimiPhilip Hazel 466*22dc650dSSadaf Ebrahimi<br> 467*22dc650dSSadaf EbrahimiRetired from University Computing Service 468*22dc650dSSadaf Ebrahimi<br> 469*22dc650dSSadaf EbrahimiCambridge, England. 470*22dc650dSSadaf Ebrahimi<br> 471*22dc650dSSadaf Ebrahimi</P> 472*22dc650dSSadaf Ebrahimi<br><a name="SEC8" href="#TOC1">REVISION</a><br> 473*22dc650dSSadaf Ebrahimi<P> 474*22dc650dSSadaf EbrahimiLast updated: 19 January 2024 475*22dc650dSSadaf Ebrahimi<br> 476*22dc650dSSadaf EbrahimiCopyright © 1997-2024 University of Cambridge. 477*22dc650dSSadaf Ebrahimi<br> 478*22dc650dSSadaf Ebrahimi<p> 479*22dc650dSSadaf EbrahimiReturn to the <a href="index.html">PCRE2 index page</a>. 480*22dc650dSSadaf Ebrahimi</p> 481