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3: <title>pcreprecompile specification</title>
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6: <h1>pcreprecompile 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">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a>
17: <li><a name="TOC2" href="#SEC2">SAVING A COMPILED PATTERN</a>
18: <li><a name="TOC3" href="#SEC3">RE-USING A PRECOMPILED PATTERN</a>
19: <li><a name="TOC4" href="#SEC4">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a>
20: <li><a name="TOC5" href="#SEC5">AUTHOR</a>
21: <li><a name="TOC6" href="#SEC6">REVISION</a>
22: </ul>
23: <br><a name="SEC1" href="#TOC1">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a><br>
24: <P>
25: If you are running an application that uses a large number of regular
26: expression patterns, it may be useful to store them in a precompiled form
27: instead of having to compile them every time the application is run.
28: If you are not using any private character tables (see the
29: <a href="pcre_maketables.html"><b>pcre_maketables()</b></a>
30: documentation), this is relatively straightforward. If you are using private
31: tables, it is a little bit more complicated. However, if you are using the
32: just-in-time optimization feature of <b>pcre_study()</b>, it is not possible to
33: save and reload the JIT data.
34: </P>
35: <P>
36: If you save compiled patterns to a file, you can copy them to a different host
37: and run them there. This works even if the new host has the opposite endianness
38: to the one on which the patterns were compiled. There may be a small
39: performance penalty, but it should be insignificant. However, compiling regular
40: expressions with one version of PCRE for use with a different version is not
41: guaranteed to work and may cause crashes, and saving and restoring a compiled
42: pattern loses any JIT optimization data.
43: </P>
44: <br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
45: <P>
46: The value returned by <b>pcre_compile()</b> points to a single block of memory
47: that holds the compiled pattern and associated data. You can find the length of
48: this block in bytes by calling <b>pcre_fullinfo()</b> with an argument of
49: PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is
50: sample code that compiles a pattern and writes it to a file. It assumes that
51: the variable <i>fd</i> refers to a file that is open for output:
52: <pre>
53: int erroroffset, rc, size;
54: char *error;
55: pcre *re;
56:
57: re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
58: if (re == NULL) { ... handle errors ... }
59: rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
60: if (rc < 0) { ... handle errors ... }
61: rc = fwrite(re, 1, size, fd);
62: if (rc != size) { ... handle errors ... }
63: </pre>
64: In this example, the bytes that comprise the compiled pattern are copied
65: exactly. Note that this is binary data that may contain any of the 256 possible
66: byte values. On systems that make a distinction between binary and non-binary
67: data, be sure that the file is opened for binary output.
68: </P>
69: <P>
70: If you want to write more than one pattern to a file, you will have to devise a
71: way of separating them. For binary data, preceding each pattern with its length
72: is probably the most straightforward approach. Another possibility is to write
73: out the data in hexadecimal instead of binary, one pattern to a line.
74: </P>
75: <P>
76: Saving compiled patterns in a file is only one possible way of storing them for
77: later use. They could equally well be saved in a database, or in the memory of
78: some daemon process that passes them via sockets to the processes that want
79: them.
80: </P>
81: <P>
82: If the pattern has been studied, it is also possible to save the normal study
83: data in a similar way to the compiled pattern itself. However, if the
84: PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is created cannot
85: be saved because it is too dependent on the current environment. When studying
86: generates additional information, <b>pcre_study()</b> returns a pointer to a
87: <b>pcre_extra</b> data block. Its format is defined in the
88: <a href="pcreapi.html#extradata">section on matching a pattern</a>
89: in the
90: <a href="pcreapi.html"><b>pcreapi</b></a>
91: documentation. The <i>study_data</i> field points to the binary study data, and
92: this is what you must save (not the <b>pcre_extra</b> block itself). The length
93: of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an
94: argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_study()</b> did
95: return a non-NULL value before trying to save the study data.
96: </P>
97: <br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
98: <P>
99: Re-using a precompiled pattern is straightforward. Having reloaded it into main
100: memory, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in
101: the usual way. This should work even on another host, and even if that host has
102: the opposite endianness to the one where the pattern was compiled.
103: </P>
104: <P>
105: However, if you passed a pointer to custom character tables when the pattern
106: was compiled (the <i>tableptr</i> argument of <b>pcre_compile()</b>), you must
107: now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>,
108: because the value saved with the compiled pattern will obviously be nonsense. A
109: field in a <b>pcre_extra()</b> block is used to pass this data, as described in
110: the
111: <a href="pcreapi.html#extradata">section on matching a pattern</a>
112: in the
113: <a href="pcreapi.html"><b>pcreapi</b></a>
114: documentation.
115: </P>
116: <P>
117: If you did not provide custom character tables when the pattern was compiled,
118: the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to
119: use PCRE's internal tables. Thus, you do not need to take any special action at
120: run time in this case.
121: </P>
122: <P>
123: If you saved study data with the compiled pattern, you need to create your own
124: <b>pcre_extra</b> data block and set the <i>study_data</i> field to point to the
125: reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
126: <i>flags</i> field to indicate that study data is present. Then pass the
127: <b>pcre_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the
128: usual way. If the pattern was studied for just-in-time optimization, that data
129: cannot be saved, and so is lost by a save/restore cycle.
130: </P>
131: <br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
132: <P>
133: In general, it is safest to recompile all saved patterns when you update to a
134: new PCRE release, though not all updates actually require this.
135: </P>
136: <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
137: <P>
138: Philip Hazel
139: <br>
140: University Computing Service
141: <br>
142: Cambridge CB2 3QH, England.
143: <br>
144: </P>
145: <br><a name="SEC6" href="#TOC1">REVISION</a><br>
146: <P>
147: Last updated: 26 August 2011
148: <br>
149: Copyright © 1997-2011 University of Cambridge.
150: <br>
151: <p>
152: Return to the <a href="index.html">PCRE index page</a>.
153: </p>
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