/[pcre]/code/trunk/doc/html/pcrepartial.html

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-revision 469 by ph10,
Mon Oct 19 14:38:48 2009 UTC
+revision 975 by ph10,
Sat Jun  2 11:03:06 2012 UTC
 Line 14 
 man page, in case the conversion went wr
  <br>
  <ul>
  <li><a name="TOC1" href="#SEC1">PARTIAL MATCHING IN PCRE</a>
- <li><a name="TOC2" href="#SEC2">PARTIAL MATCHING USING pcre_exec()</a>
+ <li><a name="TOC2" href="#SEC2">PARTIAL MATCHING USING pcre_exec() OR pcre16_exec()</a>
- <li><a name="TOC3" href="#SEC3">PARTIAL MATCHING USING pcre_dfa_exec()</a>
+ <li><a name="TOC3" href="#SEC3">PARTIAL MATCHING USING pcre_dfa_exec() OR pcre16_dfa_exec()</a>
  <li><a name="TOC4" href="#SEC4">PARTIAL MATCHING AND WORD BOUNDARIES</a>
  <li><a name="TOC5" href="#SEC5">FORMERLY RESTRICTED PATTERNS</a>
  <li><a name="TOC6" href="#SEC6">EXAMPLE OF PARTIAL MATCHING USING PCRETEST</a>
- <li><a name="TOC7" href="#SEC7">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()</a>
+ <li><a name="TOC7" href="#SEC7">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_dfa_exec()</a>
- <li><a name="TOC8" href="#SEC8">MULTI-SEGMENT MATCHING WITH pcre_exec()</a>
+ <li><a name="TOC8" href="#SEC8">MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre16_exec()</a>
  <li><a name="TOC9" href="#SEC9">ISSUES WITH MULTI-SEGMENT MATCHING</a>
  <li><a name="TOC10" href="#SEC10">AUTHOR</a>
  <li><a name="TOC11" href="#SEC11">REVISION</a>
  </ul>
  <br><a name="SEC1" href="#TOC1">PARTIAL MATCHING IN PCRE</a><br>
  <P>
- In normal use of PCRE, if the subject string that is passed to
+ In normal use of PCRE, if the subject string that is passed to a matching
- <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> matches as far as it goes, but is
+ function matches as far as it goes, but is too short to match the entire
- too short to match the entire pattern, PCRE_ERROR_NOMATCH is returned. There
+ pattern, PCRE_ERROR_NOMATCH is returned. There are circumstances where it might
- are circumstances where it might be helpful to distinguish this case from other
+ be helpful to distinguish this case from other cases in which there is no
- cases in which there is no match.
+ match.
  </P>
  <P>
  Consider, for example, an application where a human is required to type in data
 Line 45 
 what has been typed so far is potentiall
  as soon as a mistake is made, by beeping and not reflecting the character that
  has been typed, for example. This immediate feedback is likely to be a better
  user interface than a check that is delayed until the entire string has been
- entered. Partial matching can also sometimes be useful when the subject string
+ entered. Partial matching can also be useful when the subject string is very
- is very long and is not all available at once.
+ long and is not all available at once.
  </P>
  <P>
  PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and
- PCRE_PARTIAL_HARD options, which can be set when calling <b>pcre_exec()</b> or
+ PCRE_PARTIAL_HARD options, which can be set when calling any of the matching
- <b>pcre_dfa_exec()</b>. For backwards compatibility, PCRE_PARTIAL is a synonym
+ functions. For backwards compatibility, PCRE_PARTIAL is a synonym for
- for PCRE_PARTIAL_SOFT. The essential difference between the two options is
+ PCRE_PARTIAL_SOFT. The essential difference between the two options is whether
- whether or not a partial match is preferred to an alternative complete match,
+ or not a partial match is preferred to an alternative complete match, though
- though the details differ between the two matching functions. If both options
+ the details differ between the two types of matching function. If both options
  are set, PCRE_PARTIAL_HARD takes precedence.
  </P>
  <P>
- Setting a partial matching option disables two of PCRE's optimizations. PCRE
+ If you want to use partial matching with just-in-time optimized code, you must
- remembers the last literal byte in a pattern, and abandons matching immediately
+ call <b>pcre_study()</b> or <b>pcre16_study()</b> with one or both of these
- if such a byte is not present in the subject string. This optimization cannot
+ options:
- be used for a subject string that might match only partially. If the pattern
+ <pre>
- was studied, PCRE knows the minimum length of a matching string, and does not
+   PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
- bother to run the matching function on shorter strings. This optimization is
+   PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
- also disabled for partial matching.
+ </pre>
- </P>
+ PCRE_STUDY_JIT_COMPILE should also be set if you are going to run non-partial
- <br><a name="SEC2" href="#TOC1">PARTIAL MATCHING USING pcre_exec()</a><br>
+ matches on the same pattern. If the appropriate JIT study mode has not been set
- <P>
+ for a match, the interpretive matching code is used.
- A partial match occurs during a call to <b>pcre_exec()</b> whenever the end of
+ </P>
- the subject string is reached successfully, but matching cannot continue
+ <P>
- because more characters are needed. However, at least one character must have
+ Setting a partial matching option disables two of PCRE's standard
- been matched. (In other words, a partial match can never be an empty string.)
+ optimizations. PCRE remembers the last literal data unit in a pattern, and
- </P>
+ abandons matching immediately if it is not present in the subject string. This
- <P>
+ optimization cannot be used for a subject string that might match only
- If PCRE_PARTIAL_SOFT is set, the partial match is remembered, but matching
+ partially. If the pattern was studied, PCRE knows the minimum length of a
- continues as normal, and other alternatives in the pattern are tried. If no
+ matching string, and does not bother to run the matching function on shorter
- complete match can be found, <b>pcre_exec()</b> returns PCRE_ERROR_PARTIAL
+ strings. This optimization is also disabled for partial matching.
- instead of PCRE_ERROR_NOMATCH. If there are at least two slots in the offsets
+ </P>
- vector, the first of them is set to the offset of the earliest character that
+ <br><a name="SEC2" href="#TOC1">PARTIAL MATCHING USING pcre_exec() OR pcre16_exec()</a><br>
- was inspected when the partial match was found. For convenience, the second
+ <P>
- offset points to the end of the string so that a substring can easily be
+ A partial match occurs during a call to <b>pcre_exec()</b> or
- identified.
+ <b>pcre16_exec()</b> when the end of the subject string is reached successfully,
+ but matching cannot continue because more characters are needed. However, at
+ least one character in the subject must have been inspected. This character
+ need not form part of the final matched string; lookbehind assertions and the
+ \K escape sequence provide ways of inspecting characters before the start of a
+ matched substring. The requirement for inspecting at least one character exists
+ because an empty string can always be matched; without such a restriction there
+ would always be a partial match of an empty string at the end of the subject.
+ </P>
+ <P>
+ If there are at least two slots in the offsets vector when a partial match is
+ returned, the first slot is set to the offset of the earliest character that
+ was inspected. For convenience, the second offset points to the end of the
+ subject so that a substring can easily be identified.
  </P>
  <P>
  For the majority of patterns, the first offset identifies the start of the
-Line 94 
 inspected while carrying out the match.
+Line 107 
 inspected while carrying out the match.
  This pattern matches "123", but only if it is preceded by "abc". If the subject
  string is "xyzabc12", the offsets after a partial match are for the substring
  "abc12", because all these characters are needed if another match is tried
- with extra characters added.
+ with extra characters added to the subject.
+ </P>
+ <P>
+ What happens when a partial match is identified depends on which of the two
+ partial matching options are set.
+ </P>
+ <br><b>
+ PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre16_exec()
+ </b><br>
+ <P>
+ If PCRE_PARTIAL_SOFT is set when <b>pcre_exec()</b> or <b>pcre16_exec()</b>
+ identifies a partial match, the partial match is remembered, but matching
+ continues as normal, and other alternatives in the pattern are tried. If no
+ complete match can be found, PCRE_ERROR_PARTIAL is returned instead of
+ PCRE_ERROR_NOMATCH.
+ </P>
+ <P>
+ This option is "soft" because it prefers a complete match over a partial match.
+ All the various matching items in a pattern behave as if the subject string is
+ potentially complete. For example, \z, \Z, and $ match at the end of the
+ subject, as normal, and for \b and \B the end of the subject is treated as a
+ non-alphanumeric.
  </P>
  <P>
  If there is more than one partial match, the first one that was found provides
-Line 104 
 the data that is returned. Consider this
+Line 138 
 the data that is returned. Consider this
  </pre>
  If this is matched against the subject string "abc123dog", both
  alternatives fail to match, but the end of the subject is reached during
- matching, so PCRE_ERROR_PARTIAL is returned instead of PCRE_ERROR_NOMATCH. The
+ matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3 and 9,
- offsets are set to 3 and 9, identifying "123dog" as the first partial match
+ identifying "123dog" as the first partial match that was found. (In this
- that was found. (In this example, there are two partial matches, because "dog"
+ example, there are two partial matches, because "dog" on its own partially
- on its own partially matches the second alternative.)
+ matches the second alternative.)
  </P>
+ <br><b>
+ PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre16_exec()
+ </b><br>
+ <P>
+ If PCRE_PARTIAL_HARD is set for <b>pcre_exec()</b> or <b>pcre16_exec()</b>,
+ PCRE_ERROR_PARTIAL is returned as soon as a partial match is found, without
+ continuing to search for possible complete matches. This option is "hard"
+ because it prefers an earlier partial match over a later complete match. For
+ this reason, the assumption is made that the end of the supplied subject string
+ may not be the true end of the available data, and so, if \z, \Z, \b, \B,
+ or $ are encountered at the end of the subject, the result is
+ PCRE_ERROR_PARTIAL, provided that at least one character in the subject has
+ been inspected.
+ </P>
+ <P>
+ Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16
+ subject strings are checked for validity. Normally, an invalid sequence
+ causes the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the
+ special case of a truncated character at the end of the subject,
+ PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when
+ PCRE_PARTIAL_HARD is set.
+ </P>
+ <br><b>
+ Comparing hard and soft partial matching
+ </b><br>
  <P>
- If PCRE_PARTIAL_HARD is set for <b>pcre_exec()</b>, it returns
+ The difference between the two partial matching options can be illustrated by a
- PCRE_ERROR_PARTIAL as soon as a partial match is found, without continuing to
+ pattern such as:
- search for possible complete matches. The difference between the two options
- can be illustrated by a pattern such as:
  <pre>
    /dog(sbody)?/
  </pre>
-Line 125 
 if the pattern is made ungreedy the resu
+Line 182 
 if the pattern is made ungreedy the resu
  <pre>
    /dog(sbody)??/
  </pre>
- In this case the result is always a complete match because <b>pcre_exec()</b>
+ In this case the result is always a complete match because that is found first,
- finds that first, and it never continues after finding a match. It might be
+ and matching never continues after finding a complete match. It might be easier
- easier to follow this explanation by thinking of the two patterns like this:
+ to follow this explanation by thinking of the two patterns like this:
  <pre>
    /dog(sbody)?/    is the same as  /dogsbody|dog/
    /dog(sbody)??/   is the same as  /dog|dogsbody/
  </pre>
- The second pattern will never match "dogsbody" when <b>pcre_exec()</b> is
+ The second pattern will never match "dogsbody", because it will always find the
- used, because it will always find the shorter match first.
+ shorter match first.
  </P>
- <br><a name="SEC3" href="#TOC1">PARTIAL MATCHING USING pcre_dfa_exec()</a><br>
+ <br><a name="SEC3" href="#TOC1">PARTIAL MATCHING USING pcre_dfa_exec() OR pcre16_dfa_exec()</a><br>
  <P>
- The <b>pcre_dfa_exec()</b> function moves along the subject string character by
+ The DFA functions move along the subject string character by character, without
- character, without backtracking, searching for all possible matches
+ backtracking, searching for all possible matches simultaneously. If the end of
- simultaneously. If the end of the subject is reached before the end of the
+ the subject is reached before the end of the pattern, there is the possibility
- pattern, there is the possibility of a partial match, again provided that at
+ of a partial match, again provided that at least one character has been
- least one character has matched.
+ inspected.
  </P>
  <P>
  When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if there
-Line 152 
 partial match was found is set as the fi
+Line 209 
 partial match was found is set as the fi
  at least two slots in the offsets vector.
  </P>
  <P>
- Because <b>pcre_dfa_exec()</b> always searches for all possible matches, and
+ Because the DFA functions always search for all possible matches, and there is
- there is no difference between greedy and ungreedy repetition, its behaviour is
+ no difference between greedy and ungreedy repetition, their behaviour is
- different from <b>pcre_exec</b> when PCRE_PARTIAL_HARD is set. Consider the
+ different from the standard functions when PCRE_PARTIAL_HARD is set. Consider
- string "dog" matched against the ungreedy pattern shown above:
+ the string "dog" matched against the ungreedy pattern shown above:
  <pre>
    /dog(sbody)??/
  </pre>
- Whereas <b>pcre_exec()</b> stops as soon as it finds the complete match for
+ Whereas the standard functions stop as soon as they find the complete match for
- "dog", <b>pcre_dfa_exec()</b> also finds the partial match for "dogsbody", and
+ "dog", the DFA functions also find the partial match for "dogsbody", and so
- so returns that when PCRE_PARTIAL_HARD is set.
+ return that when PCRE_PARTIAL_HARD is set.
  </P>
  <br><a name="SEC4" href="#TOC1">PARTIAL MATCHING AND WORD BOUNDARIES</a><br>
  <P>
-Line 173 
 results. Consider this pattern:
+Line 230 
 results. Consider this pattern:
  </pre>
  This matches "cat", provided there is a word boundary at either end. If the
  subject string is "the cat", the comparison of the final "t" with a following
- character cannot take place, so a partial match is found. However,
+ character cannot take place, so a partial match is found. However, normal
- <b>pcre_exec()</b> carries on with normal matching, which matches \b at the end
+ matching carries on, and \b matches at the end of the subject when the last
- of the subject when the last character is a letter, thus finding a complete
+ character is a letter, so a complete match is found. The result, therefore, is
- match. The result, therefore, is <i>not</i> PCRE_ERROR_PARTIAL. The same thing
+ <i>not</i> PCRE_ERROR_PARTIAL. Using PCRE_PARTIAL_HARD in this case does yield
- happens with <b>pcre_dfa_exec()</b>, because it also finds the complete match.
+ PCRE_ERROR_PARTIAL, because then the partial match takes precedence.
- </P>
- <P>
- Using PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because
- then the partial match takes precedence.
  </P>
  <br><a name="SEC5" href="#TOC1">FORMERLY RESTRICTED PATTERNS</a><br>
  <P>
-Line 189 
 For releases of PCRE prior to 8.00, beca
+Line 242 
 For releases of PCRE prior to 8.00, beca
  optimizations were implemented in the <b>pcre_exec()</b> function, the
  PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be used with
  all patterns. From release 8.00 onwards, the restrictions no longer apply, and
- partial matching with <b>pcre_exec()</b> can be requested for any pattern.
+ partial matching with can be requested for any pattern.
  </P>
  <P>
  Items that were formerly restricted were repeated single characters and
-Line 221 
 that uses the date example quoted above:
+Line 274 
 that uses the date example quoted above:
  The first data string is matched completely, so <b>pcretest</b> shows the
  matched substrings. The remaining four strings do not match the complete
  pattern, but the first two are partial matches. Similar output is obtained
- when <b>pcre_dfa_exec()</b> is used.
+ if DFA matching is used.
  </P>
  <P>
  If the escape sequence \P is present more than once in a <b>pcretest</b> data
  line, the PCRE_PARTIAL_HARD option is set for the match.
  </P>
- <br><a name="SEC7" href="#TOC1">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()</a><br>
+ <br><a name="SEC7" href="#TOC1">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_dfa_exec()</a><br>
  <P>
- When a partial match has been found using <b>pcre_dfa_exec()</b>, it is possible
+ When a partial match has been found using a DFA matching function, it is
- to continue the match by providing additional subject data and calling
+ possible to continue the match by providing additional subject data and calling
- <b>pcre_dfa_exec()</b> again with the same compiled regular expression, this
+ the function again with the same compiled regular expression, this time setting
- time setting the PCRE_DFA_RESTART option. You must pass the same working
+ the PCRE_DFA_RESTART option. You must pass the same working space as before,
- space as before, because this is where details of the previous partial match
+ because this is where details of the previous partial match are stored. Here is
- are stored. Here is an example using <b>pcretest</b>, using the \R escape
+ an example using <b>pcretest</b>, using the \R escape sequence to set the
- sequence to set the PCRE_DFA_RESTART option (\D specifies the use of
+ PCRE_DFA_RESTART option (\D specifies the use of the DFA matching function):
- <b>pcre_dfa_exec()</b>):
  <pre>
      re&#62; /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
    data&#62; 23ja\P\D
-Line 253 
 program to do that if it needs to.
+Line 305 
 program to do that if it needs to.
  <P>
  You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with
  PCRE_DFA_RESTART to continue partial matching over multiple segments. This
- facility can be used to pass very long subject strings to
+ facility can be used to pass very long subject strings to the DFA matching
- <b>pcre_dfa_exec()</b>.
+ functions.
+ </P>
+ <br><a name="SEC8" href="#TOC1">MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre16_exec()</a><br>
+ <P>
+ From release 8.00, the standard matching functions can also be used to do
+ multi-segment matching. Unlike the DFA functions, it is not possible to
+ restart the previous match with a new segment of data. Instead, new data must
+ be added to the previous subject string, and the entire match re-run, starting
+ from the point where the partial match occurred. Earlier data can be discarded.
  </P>
- <br><a name="SEC8" href="#TOC1">MULTI-SEGMENT MATCHING WITH pcre_exec()</a><br>
  <P>
- From release 8.00, <b>pcre_exec()</b> can also be used to do multi-segment
+ It is best to use PCRE_PARTIAL_HARD in this situation, because it does not
- matching. Unlike <b>pcre_dfa_exec()</b>, it is not possible to restart the
+ treat the end of a segment as the end of the subject when matching \z, \Z,
- previous match with a new segment of data. Instead, new data must be added to
+ \b, \B, and $. Consider an unanchored pattern that matches dates:
- the previous subject string, and the entire match re-run, starting from the
- point where the partial match occurred. Earlier data can be discarded.
- Consider an unanchored pattern that matches dates:
  <pre>
      re&#62; /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/
-   data&#62; The date is 23ja\P
+   data&#62; The date is 23ja\P\P
    Partial match: 23ja
  </pre>
  At this stage, an application could discard the text preceding "23ja", add on
- text from the next segment, and call <b>pcre_exec()</b> again. Unlike
+ text from the next segment, and call the matching function again. Unlike the
- <b>pcre_dfa_exec()</b>, the entire matching string must always be available, and
+ DFA matching functions, the entire matching string must always be available,
- the complete matching process occurs for each call, so more memory and more
+ and the complete matching process occurs for each call, so more memory and more
  processing time is needed.
  </P>
  <P>
  <b>Note:</b> If the pattern contains lookbehind assertions, or \K, or starts
- with \b or \B, the string that is returned for a partial match will include
+ with \b or \B, the string that is returned for a partial match includes
  characters that precede the partially matched string itself, because these must
  be retained when adding on more characters for a subsequent matching attempt.
+ However, in some cases you may need to retain even earlier characters, as
+ discussed in the next section.
  </P>
  <br><a name="SEC9" href="#TOC1">ISSUES WITH MULTI-SEGMENT MATCHING</a><br>
  <P>
-Line 287 
 Certain types of pattern may give proble
+Line 345 
 Certain types of pattern may give proble
  whichever matching function is used.
  </P>
  <P>
-. If the pattern contains tests for the beginning or end of a line, you need
+. If the pattern contains a test for the beginning of a line, you need to pass
- to pass the PCRE_NOTBOL or PCRE_NOTEOL options, as appropriate, when the
+ the PCRE_NOTBOL option when the subject string for any call does start at the
- subject string for any call does not contain the beginning or end of a line.
+ beginning of a line. There is also a PCRE_NOTEOL option, but in practice when
- </P>
+ doing multi-segment matching you should be using PCRE_PARTIAL_HARD, which
- <P>
+ includes the effect of PCRE_NOTEOL.
-. Lookbehind assertions at the start of a pattern are catered for in the
+ </P>
- offsets that are returned for a partial match. However, in theory, a lookbehind
+ <P>
- assertion later in the pattern could require even earlier characters to be
+. Lookbehind assertions that have already been obeyed are catered for in the
- inspected, and it might not have been reached when a partial match occurs. This
+ offsets that are returned for a partial match. However a lookbehind assertion
- is probably an extremely unlikely case; you could guard against it to a certain
+ later in the pattern could require even earlier characters to be inspected. You
- extent by always including extra characters at the start.
+ can handle this case by using the PCRE_INFO_MAXLOOKBEHIND option of the
+ <b>pcre_fullinfo()</b> or <b>pcre16_fullinfo()</b> functions to obtain the length
+ of the largest lookbehind in the pattern. This length is given in characters,
+ not bytes. If you always retain at least that many characters before the
+ partially matched string, all should be well. (Of course, near the start of the
+ subject, fewer characters may be present; in that case all characters should be
+ retained.)
+ </P>
+ <P>
+. Because a partial match must always contain at least one character, what
+ might be considered a partial match of an empty string actually gives a "no
+ match" result. For example:
+ <pre>
+     re&#62; /c(?&#60;=abc)x/
+   data&#62; ab\P
+   No match
+ </pre>
+ If the next segment begins "cx", a match should be found, but this will only
+ happen if characters from the previous segment are retained. For this reason, a
+ "no match" result should be interpreted as "partial match of an empty string"
+ when the pattern contains lookbehinds.
  </P>
  <P>
 . Matching a subject string that is split into multiple segments may not
  always produce exactly the same result as matching over one single long string,
  especially when PCRE_PARTIAL_SOFT is used. The section "Partial Matching and
  Word Boundaries" above describes an issue that arises if the pattern ends with
  \b or \B. Another kind of difference may occur when there are multiple
- matching possibilities, because a partial match result is given only when there
+ matching possibilities, because (for PCRE_PARTIAL_SOFT) a partial match result
- are no completed matches. This means that as soon as the shortest match has
+ is given only when there are no completed matches. This means that as soon as
- been found, continuation to a new subject segment is no longer possible.
+ the shortest match has been found, continuation to a new subject segment is no
- Consider again this <b>pcretest</b> example:
+ longer possible. Consider again this <b>pcretest</b> example:
  <pre>
      re&#62; /dog(sbody)?/
    data&#62; dogsb\P
-Line 321 
 Consider again this pcretest exam
+Line 399 
 Consider again this pcretest exam
 : dogsbody
 : dog
  </pre>
- The first data line passes the string "dogsb" to <b>pcre_exec()</b>, setting the
+ The first data line passes the string "dogsb" to a standard matching function,
- PCRE_PARTIAL_SOFT option. Although the string is a partial match for
+ setting the PCRE_PARTIAL_SOFT option. Although the string is a partial match
- "dogsbody", the result is not PCRE_ERROR_PARTIAL, because the shorter string
+ for "dogsbody", the result is not PCRE_ERROR_PARTIAL, because the shorter
- "dog" is a complete match. Similarly, when the subject is presented to
+ string "dog" is a complete match. Similarly, when the subject is presented to
- <b>pcre_dfa_exec()</b> in several parts ("do" and "gsb" being the first two) the
+ a DFA matching function in several parts ("do" and "gsb" being the first two)
- match stops when "dog" has been found, and it is not possible to continue. On
+ the match stops when "dog" has been found, and it is not possible to continue.
- the other hand, if "dogsbody" is presented as a single string,
+ On the other hand, if "dogsbody" is presented as a single string, a DFA
- <b>pcre_dfa_exec()</b> finds both matches.
+ matching function finds both matches.
  </P>
  <P>
- Because of these problems, it is probably best to use PCRE_PARTIAL_HARD when
+ Because of these problems, it is best to use PCRE_PARTIAL_HARD when matching
- matching multi-segment data. The example above then behaves differently:
+ multi-segment data. The example above then behaves differently:
  <pre>
      re&#62; /dog(sbody)?/
    data&#62; dogsb\P\P
-Line 341 
 matching multi-segment data. The example
+Line 419 
 matching multi-segment data. The example
    Partial match: do
    data&#62; gsb\R\P\P\D
    Partial match: gsb
+ </pre>
- </PRE>
+. Patterns that contain alternatives at the top level which do not all start
- </P>
+ with the same pattern item may not work as expected when PCRE_DFA_RESTART is
- <P>
+ used. For example, consider this pattern:
-. Patterns that contain alternatives at the top level which do not all
- start with the same pattern item may not work as expected when
- PCRE_DFA_RESTART is used with <b>pcre_dfa_exec()</b>. For example, consider this
- pattern:
  <pre>
 |3789
  </pre>
-Line 364 
 patterns or patterns such as:
+Line 438 
 patterns or patterns such as:
 |ABCD
  </pre>
  where no string can be a partial match for both alternatives. This is not a
- problem if <b>pcre_exec()</b> is used, because the entire match has to be rerun
+ problem if a standard matching function is used, because the entire match has
- each time:
+ to be rerun each time:
  <pre>
      re&#62; /1234|3789/
-   data&#62; ABC123\P
+   data&#62; ABC123\P\P
    Partial match: 123
    data&#62; 1237890
 : 3789
  </pre>
- Of course, instead of using PCRE_DFA_PARTIAL, the same technique of re-running
+ Of course, instead of using PCRE_DFA_RESTART, the same technique of re-running
- the entire match can also be used with <b>pcre_dfa_exec()</b>. Another
+ the entire match can also be used with the DFA matching functions. Another
  possibility is to work with two buffers. If a partial match at offset <i>n</i>
  in the first buffer is followed by "no match" when PCRE_DFA_RESTART is used on
  the second buffer, you can then try a new match starting at offset <i>n+1</i> in
-Line 391 
 Cambridge CB2 3QH, England.
+Line 465 
 Cambridge CB2 3QH, England.
  </P>
  <br><a name="SEC11" href="#TOC1">REVISION</a><br>
  <P>
- Last updated: 19 October 2009
+ Last updated: 24 February 2012
  <br>
- Copyright &copy; 1997-2009 University of Cambridge.
+ Copyright &copy; 1997-2012 University of Cambridge.
  <br>
  <p>
  Return to the <a href="index.html">PCRE index page</a>.

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