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    1 <html>
    2 <head>
    3 <title>pcrepartial specification</title>
    4 </head>
    5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
    6 <h1>pcrepartial man page</h1>
    7 <p>
    8 Return to the <a href="index.html">PCRE index page</a>.
    9 </p>
   10 <p>
   11 This page is part of the PCRE HTML documentation. It was generated automatically
   12 from the original man page. If there is any nonsense in it, please consult the
   13 man page, in case the conversion went wrong.
   14 <br>
   15 <ul>
   16 <li><a name="TOC1" href="#SEC1">PARTIAL MATCHING IN PCRE</a>
   17 <li><a name="TOC2" href="#SEC2">PARTIAL MATCHING USING pcre_exec() OR pcre[16|32]_exec()</a>
   18 <li><a name="TOC3" href="#SEC3">PARTIAL MATCHING USING pcre_dfa_exec() OR pcre[16|32]_dfa_exec()</a>
   19 <li><a name="TOC4" href="#SEC4">PARTIAL MATCHING AND WORD BOUNDARIES</a>
   20 <li><a name="TOC5" href="#SEC5">FORMERLY RESTRICTED PATTERNS</a>
   21 <li><a name="TOC6" href="#SEC6">EXAMPLE OF PARTIAL MATCHING USING PCRETEST</a>
   22 <li><a name="TOC7" href="#SEC7">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre[16|32]_dfa_exec()</a>
   23 <li><a name="TOC8" href="#SEC8">MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre[16|32]_exec()</a>
   24 <li><a name="TOC9" href="#SEC9">ISSUES WITH MULTI-SEGMENT MATCHING</a>
   25 <li><a name="TOC10" href="#SEC10">AUTHOR</a>
   26 <li><a name="TOC11" href="#SEC11">REVISION</a>
   27 </ul>
   28 <br><a name="SEC1" href="#TOC1">PARTIAL MATCHING IN PCRE</a><br>
   29 <P>
   30 In normal use of PCRE, if the subject string that is passed to a matching
   31 function matches as far as it goes, but is too short to match the entire
   32 pattern, PCRE_ERROR_NOMATCH is returned. There are circumstances where it might
   33 be helpful to distinguish this case from other cases in which there is no
   34 match.
   35 </P>
   36 <P>
   37 Consider, for example, an application where a human is required to type in data
   38 for a field with specific formatting requirements. An example might be a date
   39 in the form <i>ddmmmyy</i>, defined by this pattern:
   40 <pre>
   41   ^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$
   42 </pre>
   43 If the application sees the user's keystrokes one by one, and can check that
   44 what has been typed so far is potentially valid, it is able to raise an error
   45 as soon as a mistake is made, by beeping and not reflecting the character that
   46 has been typed, for example. This immediate feedback is likely to be a better
   47 user interface than a check that is delayed until the entire string has been
   48 entered. Partial matching can also be useful when the subject string is very
   49 long and is not all available at once.
   50 </P>
   51 <P>
   52 PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and
   53 PCRE_PARTIAL_HARD options, which can be set when calling any of the matching
   54 functions. For backwards compatibility, PCRE_PARTIAL is a synonym for
   55 PCRE_PARTIAL_SOFT. The essential difference between the two options is whether
   56 or not a partial match is preferred to an alternative complete match, though
   57 the details differ between the two types of matching function. If both options
   58 are set, PCRE_PARTIAL_HARD takes precedence.
   59 </P>
   60 <P>
   61 If you want to use partial matching with just-in-time optimized code, you must
   62 call <b>pcre_study()</b>, <b>pcre16_study()</b> or  <b>pcre32_study()</b> with one
   63 or both of these options:
   64 <pre>
   65   PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
   66   PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
   67 </pre>
   68 PCRE_STUDY_JIT_COMPILE should also be set if you are going to run non-partial
   69 matches on the same pattern. If the appropriate JIT study mode has not been set
   70 for a match, the interpretive matching code is used.
   71 </P>
   72 <P>
   73 Setting a partial matching option disables two of PCRE's standard
   74 optimizations. PCRE remembers the last literal data unit in a pattern, and
   75 abandons matching immediately if it is not present in the subject string. This
   76 optimization cannot be used for a subject string that might match only
   77 partially. If the pattern was studied, PCRE knows the minimum length of a
   78 matching string, and does not bother to run the matching function on shorter
   79 strings. This optimization is also disabled for partial matching.
   80 </P>
   81 <br><a name="SEC2" href="#TOC1">PARTIAL MATCHING USING pcre_exec() OR pcre[16|32]_exec()</a><br>
   82 <P>
   83 A partial match occurs during a call to <b>pcre_exec()</b> or
   84 <b>pcre[16|32]_exec()</b> when the end of the subject string is reached
   85 successfully, but matching cannot continue because more characters are needed.
   86 However, at least one character in the subject must have been inspected. This
   87 character need not form part of the final matched string; lookbehind assertions
   88 and the \K escape sequence provide ways of inspecting characters before the
   89 start of a matched substring. The requirement for inspecting at least one
   90 character exists because an empty string can always be matched; without such a
   91 restriction there would always be a partial match of an empty string at the end
   92 of the subject.
   93 </P>
   94 <P>
   95 If there are at least two slots in the offsets vector when a partial match is
   96 returned, the first slot is set to the offset of the earliest character that
   97 was inspected. For convenience, the second offset points to the end of the
   98 subject so that a substring can easily be identified. If there are at least
   99 three slots in the offsets vector, the third slot is set to the offset of the
  100 character where matching started.
  101 </P>
  102 <P>
  103 For the majority of patterns, the contents of the first and third slots will be
  104 the same. However, for patterns that contain lookbehind assertions, or begin
  105 with \b or \B, characters before the one where matching started may have been
  106 inspected while carrying out the match. For example, consider this pattern:
  107 <pre>
  108   /(?&#60;=abc)123/
  109 </pre>
  110 This pattern matches "123", but only if it is preceded by "abc". If the subject
  111 string is "xyzabc12", the first two offsets after a partial match are for the
  112 substring "abc12", because all these characters were inspected. However, the
  113 third offset is set to 6, because that is the offset where matching began.
  114 </P>
  115 <P>
  116 What happens when a partial match is identified depends on which of the two
  117 partial matching options are set.
  118 </P>
  119 <br><b>
  120 PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre[16|32]_exec()
  121 </b><br>
  122 <P>
  123 If PCRE_PARTIAL_SOFT is set when <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b>
  124 identifies a partial match, the partial match is remembered, but matching
  125 continues as normal, and other alternatives in the pattern are tried. If no
  126 complete match can be found, PCRE_ERROR_PARTIAL is returned instead of
  127 PCRE_ERROR_NOMATCH.
  128 </P>
  129 <P>
  130 This option is "soft" because it prefers a complete match over a partial match.
  131 All the various matching items in a pattern behave as if the subject string is
  132 potentially complete. For example, \z, \Z, and $ match at the end of the
  133 subject, as normal, and for \b and \B the end of the subject is treated as a
  134 non-alphanumeric.
  135 </P>
  136 <P>
  137 If there is more than one partial match, the first one that was found provides
  138 the data that is returned. Consider this pattern:
  139 <pre>
  140   /123\w+X|dogY/
  141 </pre>
  142 If this is matched against the subject string "abc123dog", both
  143 alternatives fail to match, but the end of the subject is reached during
  144 matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3 and 9,
  145 identifying "123dog" as the first partial match that was found. (In this
  146 example, there are two partial matches, because "dog" on its own partially
  147 matches the second alternative.)
  148 </P>
  149 <br><b>
  150 PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre[16|32]_exec()
  151 </b><br>
  152 <P>
  153 If PCRE_PARTIAL_HARD is set for <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b>,
  154 PCRE_ERROR_PARTIAL is returned as soon as a partial match is found, without
  155 continuing to search for possible complete matches. This option is "hard"
  156 because it prefers an earlier partial match over a later complete match. For
  157 this reason, the assumption is made that the end of the supplied subject string
  158 may not be the true end of the available data, and so, if \z, \Z, \b, \B,
  159 or $ are encountered at the end of the subject, the result is
  160 PCRE_ERROR_PARTIAL, provided that at least one character in the subject has
  161 been inspected.
  162 </P>
  163 <P>
  164 Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16
  165 subject strings are checked for validity. Normally, an invalid sequence
  166 causes the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the
  167 special case of a truncated character at the end of the subject,
  168 PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when
  169 PCRE_PARTIAL_HARD is set.
  170 </P>
  171 <br><b>
  172 Comparing hard and soft partial matching
  173 </b><br>
  174 <P>
  175 The difference between the two partial matching options can be illustrated by a
  176 pattern such as:
  177 <pre>
  178   /dog(sbody)?/
  179 </pre>
  180 This matches either "dog" or "dogsbody", greedily (that is, it prefers the
  181 longer string if possible). If it is matched against the string "dog" with
  182 PCRE_PARTIAL_SOFT, it yields a complete match for "dog". However, if
  183 PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL. On the other hand,
  184 if the pattern is made ungreedy the result is different:
  185 <pre>
  186   /dog(sbody)??/
  187 </pre>
  188 In this case the result is always a complete match because that is found first,
  189 and matching never continues after finding a complete match. It might be easier
  190 to follow this explanation by thinking of the two patterns like this:
  191 <pre>
  192   /dog(sbody)?/    is the same as  /dogsbody|dog/
  193   /dog(sbody)??/   is the same as  /dog|dogsbody/
  194 </pre>
  195 The second pattern will never match "dogsbody", because it will always find the
  196 shorter match first.
  197 </P>
  198 <br><a name="SEC3" href="#TOC1">PARTIAL MATCHING USING pcre_dfa_exec() OR pcre[16|32]_dfa_exec()</a><br>
  199 <P>
  200 The DFA functions move along the subject string character by character, without
  201 backtracking, searching for all possible matches simultaneously. If the end of
  202 the subject is reached before the end of the pattern, there is the possibility
  203 of a partial match, again provided that at least one character has been
  204 inspected.
  205 </P>
  206 <P>
  207 When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if there
  208 have been no complete matches. Otherwise, the complete matches are returned.
  209 However, if PCRE_PARTIAL_HARD is set, a partial match takes precedence over any
  210 complete matches. The portion of the string that was inspected when the longest
  211 partial match was found is set as the first matching string, provided there are
  212 at least two slots in the offsets vector.
  213 </P>
  214 <P>
  215 Because the DFA functions always search for all possible matches, and there is
  216 no difference between greedy and ungreedy repetition, their behaviour is
  217 different from the standard functions when PCRE_PARTIAL_HARD is set. Consider
  218 the string "dog" matched against the ungreedy pattern shown above:
  219 <pre>
  220   /dog(sbody)??/
  221 </pre>
  222 Whereas the standard functions stop as soon as they find the complete match for
  223 "dog", the DFA functions also find the partial match for "dogsbody", and so
  224 return that when PCRE_PARTIAL_HARD is set.
  225 </P>
  226 <br><a name="SEC4" href="#TOC1">PARTIAL MATCHING AND WORD BOUNDARIES</a><br>
  227 <P>
  228 If a pattern ends with one of sequences \b or \B, which test for word
  229 boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter-intuitive
  230 results. Consider this pattern:
  231 <pre>
  232   /\bcat\b/
  233 </pre>
  234 This matches "cat", provided there is a word boundary at either end. If the
  235 subject string is "the cat", the comparison of the final "t" with a following
  236 character cannot take place, so a partial match is found. However, normal
  237 matching carries on, and \b matches at the end of the subject when the last
  238 character is a letter, so a complete match is found. The result, therefore, is
  239 <i>not</i> PCRE_ERROR_PARTIAL. Using PCRE_PARTIAL_HARD in this case does yield
  240 PCRE_ERROR_PARTIAL, because then the partial match takes precedence.
  241 </P>
  242 <br><a name="SEC5" href="#TOC1">FORMERLY RESTRICTED PATTERNS</a><br>
  243 <P>
  244 For releases of PCRE prior to 8.00, because of the way certain internal
  245 optimizations were implemented in the <b>pcre_exec()</b> function, the
  246 PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be used with
  247 all patterns. From release 8.00 onwards, the restrictions no longer apply, and
  248 partial matching with can be requested for any pattern.
  249 </P>
  250 <P>
  251 Items that were formerly restricted were repeated single characters and
  252 repeated metasequences. If PCRE_PARTIAL was set for a pattern that did not
  253 conform to the restrictions, <b>pcre_exec()</b> returned the error code
  254 PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The
  255 PCRE_INFO_OKPARTIAL call to <b>pcre_fullinfo()</b> to find out if a compiled
  256 pattern can be used for partial matching now always returns 1.
  257 </P>
  258 <br><a name="SEC6" href="#TOC1">EXAMPLE OF PARTIAL MATCHING USING PCRETEST</a><br>
  259 <P>
  260 If the escape sequence \P is present in a <b>pcretest</b> data line, the
  261 PCRE_PARTIAL_SOFT option is used for the match. Here is a run of <b>pcretest</b>
  262 that uses the date example quoted above:
  263 <pre>
  264     re&#62; /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
  265   data&#62; 25jun04\P
  266    0: 25jun04
  267    1: jun
  268   data&#62; 25dec3\P
  269   Partial match: 23dec3
  270   data&#62; 3ju\P
  271   Partial match: 3ju
  272   data&#62; 3juj\P
  273   No match
  274   data&#62; j\P
  275   No match
  276 </pre>
  277 The first data string is matched completely, so <b>pcretest</b> shows the
  278 matched substrings. The remaining four strings do not match the complete
  279 pattern, but the first two are partial matches. Similar output is obtained
  280 if DFA matching is used.
  281 </P>
  282 <P>
  283 If the escape sequence \P is present more than once in a <b>pcretest</b> data
  284 line, the PCRE_PARTIAL_HARD option is set for the match.
  285 </P>
  286 <br><a name="SEC7" href="#TOC1">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre[16|32]_dfa_exec()</a><br>
  287 <P>
  288 When a partial match has been found using a DFA matching function, it is
  289 possible to continue the match by providing additional subject data and calling
  290 the function again with the same compiled regular expression, this time setting
  291 the PCRE_DFA_RESTART option. You must pass the same working space as before,
  292 because this is where details of the previous partial match are stored. Here is
  293 an example using <b>pcretest</b>, using the \R escape sequence to set the
  294 PCRE_DFA_RESTART option (\D specifies the use of the DFA matching function):
  295 <pre>
  296     re&#62; /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
  297   data&#62; 23ja\P\D
  298   Partial match: 23ja
  299   data&#62; n05\R\D
  300    0: n05
  301 </pre>
  302 The first call has "23ja" as the subject, and requests partial matching; the
  303 second call has "n05" as the subject for the continued (restarted) match.
  304 Notice that when the match is complete, only the last part is shown; PCRE does
  305 not retain the previously partially-matched string. It is up to the calling
  306 program to do that if it needs to.
  307 </P>
  308 <P>
  309 That means that, for an unanchored pattern, if a continued match fails, it is
  310 not possible to try again at a new starting point. All this facility is capable
  311 of doing is continuing with the previous match attempt. In the previous
  312 example, if the second set of data is "ug23" the result is no match, even
  313 though there would be a match for "aug23" if the entire string were given at
  314 once. Depending on the application, this may or may not be what you want.
  315 The only way to allow for starting again at the next character is to retain the
  316 matched part of the subject and try a new complete match.
  317 </P>
  318 <P>
  319 You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with
  320 PCRE_DFA_RESTART to continue partial matching over multiple segments. This
  321 facility can be used to pass very long subject strings to the DFA matching
  322 functions.
  323 </P>
  324 <br><a name="SEC8" href="#TOC1">MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre[16|32]_exec()</a><br>
  325 <P>
  326 From release 8.00, the standard matching functions can also be used to do
  327 multi-segment matching. Unlike the DFA functions, it is not possible to
  328 restart the previous match with a new segment of data. Instead, new data must
  329 be added to the previous subject string, and the entire match re-run, starting
  330 from the point where the partial match occurred. Earlier data can be discarded.
  331 </P>
  332 <P>
  333 It is best to use PCRE_PARTIAL_HARD in this situation, because it does not
  334 treat the end of a segment as the end of the subject when matching \z, \Z,
  335 \b, \B, and $. Consider an unanchored pattern that matches dates:
  336 <pre>
  337     re&#62; /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/
  338   data&#62; The date is 23ja\P\P
  339   Partial match: 23ja
  340 </pre>
  341 At this stage, an application could discard the text preceding "23ja", add on
  342 text from the next segment, and call the matching function again. Unlike the
  343 DFA matching functions, the entire matching string must always be available,
  344 and the complete matching process occurs for each call, so more memory and more
  345 processing time is needed.
  346 </P>
  347 <P>
  348 <b>Note:</b> If the pattern contains lookbehind assertions, or \K, or starts
  349 with \b or \B, the string that is returned for a partial match includes
  350 characters that precede the start of what would be returned for a complete
  351 match, because it contains all the characters that were inspected during the
  352 partial match.
  353 </P>
  354 <br><a name="SEC9" href="#TOC1">ISSUES WITH MULTI-SEGMENT MATCHING</a><br>
  355 <P>
  356 Certain types of pattern may give problems with multi-segment matching,
  357 whichever matching function is used.
  358 </P>
  359 <P>
  360 1. If the pattern contains a test for the beginning of a line, you need to pass
  361 the PCRE_NOTBOL option when the subject string for any call does start at the
  362 beginning of a line. There is also a PCRE_NOTEOL option, but in practice when
  363 doing multi-segment matching you should be using PCRE_PARTIAL_HARD, which
  364 includes the effect of PCRE_NOTEOL.
  365 </P>
  366 <P>
  367 2. Lookbehind assertions that have already been obeyed are catered for in the
  368 offsets that are returned for a partial match. However a lookbehind assertion
  369 later in the pattern could require even earlier characters to be inspected. You
  370 can handle this case by using the PCRE_INFO_MAXLOOKBEHIND option of the
  371 <b>pcre_fullinfo()</b> or <b>pcre[16|32]_fullinfo()</b> functions to obtain the
  372 length of the longest lookbehind in the pattern. This length is given in
  373 characters, not bytes. If you always retain at least that many characters
  374 before the partially matched string, all should be well. (Of course, near the
  375 start of the subject, fewer characters may be present; in that case all
  376 characters should be retained.)
  377 </P>
  378 <P>
  379 From release 8.33, there is a more accurate way of deciding which characters to
  380 retain. Instead of subtracting the length of the longest lookbehind from the
  381 earliest inspected character (<i>offsets[0]</i>), the match start position
  382 (<i>offsets[2]</i>) should be used, and the next match attempt started at the
  383 <i>offsets[2]</i> character by setting the <i>startoffset</i> argument of
  384 <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>.
  385 </P>
  386 <P>
  387 For example, if the pattern "(?&#60;=123)abc" is partially
  388 matched against the string "xx123a", the three offset values returned are 2, 6,
  389 and 5. This indicates that the matching process that gave a partial match
  390 started at offset 5, but the characters "123a" were all inspected. The maximum
  391 lookbehind for that pattern is 3, so taking that away from 5 shows that we need
  392 only keep "123a", and the next match attempt can be started at offset 3 (that
  393 is, at "a") when further characters have been added. When the match start is
  394 not the earliest inspected character, <b>pcretest</b> shows it explicitly:
  395 <pre>
  396     re&#62; "(?&#60;=123)abc"
  397   data&#62; xx123a\P\P
  398   Partial match at offset 5: 123a
  399 </PRE>
  400 </P>
  401 <P>
  402 3. Because a partial match must always contain at least one character, what
  403 might be considered a partial match of an empty string actually gives a "no
  404 match" result. For example:
  405 <pre>
  406     re&#62; /c(?&#60;=abc)x/
  407   data&#62; ab\P
  408   No match
  409 </pre>
  410 If the next segment begins "cx", a match should be found, but this will only
  411 happen if characters from the previous segment are retained. For this reason, a
  412 "no match" result should be interpreted as "partial match of an empty string"
  413 when the pattern contains lookbehinds.
  414 </P>
  415 <P>
  416 4. Matching a subject string that is split into multiple segments may not
  417 always produce exactly the same result as matching over one single long string,
  418 especially when PCRE_PARTIAL_SOFT is used. The section "Partial Matching and
  419 Word Boundaries" above describes an issue that arises if the pattern ends with
  420 \b or \B. Another kind of difference may occur when there are multiple
  421 matching possibilities, because (for PCRE_PARTIAL_SOFT) a partial match result
  422 is given only when there are no completed matches. This means that as soon as
  423 the shortest match has been found, continuation to a new subject segment is no
  424 longer possible. Consider again this <b>pcretest</b> example:
  425 <pre>
  426     re&#62; /dog(sbody)?/
  427   data&#62; dogsb\P
  428    0: dog
  429   data&#62; do\P\D
  430   Partial match: do
  431   data&#62; gsb\R\P\D
  432    0: g
  433   data&#62; dogsbody\D
  434    0: dogsbody
  435    1: dog
  436 </pre>
  437 The first data line passes the string "dogsb" to a standard matching function,
  438 setting the PCRE_PARTIAL_SOFT option. Although the string is a partial match
  439 for "dogsbody", the result is not PCRE_ERROR_PARTIAL, because the shorter
  440 string "dog" is a complete match. Similarly, when the subject is presented to
  441 a DFA matching function in several parts ("do" and "gsb" being the first two)
  442 the match stops when "dog" has been found, and it is not possible to continue.
  443 On the other hand, if "dogsbody" is presented as a single string, a DFA
  444 matching function finds both matches.
  445 </P>
  446 <P>
  447 Because of these problems, it is best to use PCRE_PARTIAL_HARD when matching
  448 multi-segment data. The example above then behaves differently:
  449 <pre>
  450     re&#62; /dog(sbody)?/
  451   data&#62; dogsb\P\P
  452   Partial match: dogsb
  453   data&#62; do\P\D
  454   Partial match: do
  455   data&#62; gsb\R\P\P\D
  456   Partial match: gsb
  457 </pre>
  458 5. Patterns that contain alternatives at the top level which do not all start
  459 with the same pattern item may not work as expected when PCRE_DFA_RESTART is
  460 used. For example, consider this pattern:
  461 <pre>
  462   1234|3789
  463 </pre>
  464 If the first part of the subject is "ABC123", a partial match of the first
  465 alternative is found at offset 3. There is no partial match for the second
  466 alternative, because such a match does not start at the same point in the
  467 subject string. Attempting to continue with the string "7890" does not yield a
  468 match because only those alternatives that match at one point in the subject
  469 are remembered. The problem arises because the start of the second alternative
  470 matches within the first alternative. There is no problem with anchored
  471 patterns or patterns such as:
  472 <pre>
  473   1234|ABCD
  474 </pre>
  475 where no string can be a partial match for both alternatives. This is not a
  476 problem if a standard matching function is used, because the entire match has
  477 to be rerun each time:
  478 <pre>
  479     re&#62; /1234|3789/
  480   data&#62; ABC123\P\P
  481   Partial match: 123
  482   data&#62; 1237890
  483    0: 3789
  484 </pre>
  485 Of course, instead of using PCRE_DFA_RESTART, the same technique of re-running
  486 the entire match can also be used with the DFA matching functions. Another
  487 possibility is to work with two buffers. If a partial match at offset <i>n</i>
  488 in the first buffer is followed by "no match" when PCRE_DFA_RESTART is used on
  489 the second buffer, you can then try a new match starting at offset <i>n+1</i> in
  490 the first buffer.
  491 </P>
  492 <br><a name="SEC10" href="#TOC1">AUTHOR</a><br>
  493 <P>
  494 Philip Hazel
  495 <br>
  496 University Computing Service
  497 <br>
  498 Cambridge CB2 3QH, England.
  499 <br>
  500 </P>
  501 <br><a name="SEC11" href="#TOC1">REVISION</a><br>
  502 <P>
  503 Last updated: 02 July 2013
  504 <br>
  505 Copyright &copy; 1997-2013 University of Cambridge.
  506 <br>
  507 <p>
  508 Return to the <a href="index.html">PCRE index page</a>.
  509 </p>