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the details differ between the two types of matching function. If both options
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are set, PCRE_PARTIAL_HARD takes precedence.
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Setting a partial matching option disables the use of any just-in-time code
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that was set up by studying the compiled pattern with the
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PCRE_STUDY_JIT_COMPILE option. It also disables two of PCRE's standard
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If you want to use partial matching with just-in-time optimized code, you must
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call \fBpcre_study()\fP or \fBpcre16_study()\fP with one or both of these
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PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
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PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
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PCRE_STUDY_JIT_COMPILE should also be set if you are going to run non-partial
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matches on the same pattern. If the appropriate JIT study mode has not been set
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for a match, the interpretive matching code is used.
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Setting a partial matching option disables two of PCRE's standard
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optimizations. PCRE remembers the last literal data unit in a pattern, and
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abandons matching immediately if it is not present in the subject string. This
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optimization cannot be used for a subject string that might match only
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At this stage, an application could discard the text preceding "23ja", add on
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text from the next segment, and call the matching function again. Unlike the
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DFA matching functions the entire matching string must always be available, and
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the complete matching process occurs for each call, so more memory and more
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DFA matching functions, the entire matching string must always be available,
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and the complete matching process occurs for each call, so more memory and more
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processing time is needed.
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\fBNote:\fP If the pattern contains lookbehind assertions, or \eK, or starts
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with \eb or \eB, the string that is returned for a partial match includes
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characters that precede the partially matched string itself, because these must
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be retained when adding on more characters for a subsequent matching attempt.
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However, in some cases you may need to retain even earlier characters, as
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discussed in the next section.
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.SH "ISSUES WITH MULTI-SEGMENT MATCHING"
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doing multi-segment matching you should be using PCRE_PARTIAL_HARD, which
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includes the effect of PCRE_NOTEOL.
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2. Lookbehind assertions at the start of a pattern are catered for in the
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offsets that are returned for a partial match. However, in theory, a lookbehind
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assertion later in the pattern could require even earlier characters to be
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inspected, and it might not have been reached when a partial match occurs. This
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is probably an extremely unlikely case; you could guard against it to a certain
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extent by always including extra characters at the start.
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3. Matching a subject string that is split into multiple segments may not
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2. Lookbehind assertions that have already been obeyed are catered for in the
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offsets that are returned for a partial match. However a lookbehind assertion
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later in the pattern could require even earlier characters to be inspected. You
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can handle this case by using the PCRE_INFO_MAXLOOKBEHIND option of the
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\fBpcre_fullinfo()\fP or \fBpcre16_fullinfo()\fP functions to obtain the length
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of the largest lookbehind in the pattern. This length is given in characters,
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not bytes. If you always retain at least that many characters before the
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partially matched string, all should be well. (Of course, near the start of the
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subject, fewer characters may be present; in that case all characters should be
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3. Because a partial match must always contain at least one character, what
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might be considered a partial match of an empty string actually gives a "no
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match" result. For example:
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If the next segment begins "cx", a match should be found, but this will only
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happen if characters from the previous segment are retained. For this reason, a
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"no match" result should be interpreted as "partial match of an empty string"
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when the pattern contains lookbehinds.
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4. Matching a subject string that is split into multiple segments may not
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always produce exactly the same result as matching over one single long string,
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especially when PCRE_PARTIAL_SOFT is used. The section "Partial Matching and
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Word Boundaries" above describes an issue that arises if the pattern ends with
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data> gsb\eR\eP\eP\eD
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Partial match: gsb
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4. Patterns that contain alternatives at the top level which do not all start
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5. Patterns that contain alternatives at the top level which do not all start
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with the same pattern item may not work as expected when PCRE_DFA_RESTART is
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used. For example, consider this pattern:
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doc/pcrepartial.3
