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1 <html>
2 <head>
3 <title>pcreprecompile specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
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>
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>
20 <li><a name="TOC5" href="#SEC5">AUTHOR</a>
21 <li><a name="TOC6" href="#SEC6">REVISION</a>
22 </ul>
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.
32 </P>
33 <P>
34 If you save compiled patterns to a file, you can copy them to a different host
35 and run them there. This works even if the new host has the opposite endianness
36 to the one on which the patterns were compiled. There may be a small
37 performance penalty, but it should be insignificant. However, compiling regular
38 expressions with one version of PCRE for use with a different version is not
39 guaranteed to work and may cause crashes.
40 </P>
41 <br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
42 <P>
43 The value returned by <b>pcre_compile()</b> points to a single block of memory
44 that holds the compiled pattern and associated data. You can find the length of
45 this block in bytes by calling <b>pcre_fullinfo()</b> with an argument of
46 PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is
47 sample code that compiles a pattern and writes it to a file. It assumes that
48 the variable <i>fd</i> refers to a file that is open for output:
49 <pre>
50 int erroroffset, rc, size;
51 char *error;
52 pcre *re;
54 re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
55 if (re == NULL) { ... handle errors ... }
56 rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
57 if (rc &#60; 0) { ... handle errors ... }
58 rc = fwrite(re, 1, size, fd);
59 if (rc != size) { ... handle errors ... }
60 </pre>
61 In this example, the bytes that comprise the compiled pattern are copied
62 exactly. Note that this is binary data that may contain any of the 256 possible
63 byte values. On systems that make a distinction between binary and non-binary
64 data, be sure that the file is opened for binary output.
65 </P>
66 <P>
67 If you want to write more than one pattern to a file, you will have to devise a
68 way of separating them. For binary data, preceding each pattern with its length
69 is probably the most straightforward approach. Another possibility is to write
70 out the data in hexadecimal instead of binary, one pattern to a line.
71 </P>
72 <P>
73 Saving compiled patterns in a file is only one possible way of storing them for
74 later use. They could equally well be saved in a database, or in the memory of
75 some daemon process that passes them via sockets to the processes that want
76 them.
77 </P>
78 <P>
79 If the pattern has been studied, it is also possible to save the study data in
80 a similar way to the compiled pattern itself. When studying generates
81 additional information, <b>pcre_study()</b> returns a pointer to a
82 <b>pcre_extra</b> data block. Its format is defined in the
83 <a href="pcreapi.html#extradata">section on matching a pattern</a>
84 in the
85 <a href="pcreapi.html"><b>pcreapi</b></a>
86 documentation. The <i>study_data</i> field points to the binary study data, and
87 this is what you must save (not the <b>pcre_extra</b> block itself). The length
88 of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an
89 argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_study()</b> did
90 return a non-NULL value before trying to save the study data.
91 </P>
92 <br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
93 <P>
94 Re-using a precompiled pattern is straightforward. Having reloaded it into main
95 memory, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in
96 the usual way. This should work even on another host, and even if that host has
97 the opposite endianness to the one where the pattern was compiled.
98 </P>
99 <P>
100 However, if you passed a pointer to custom character tables when the pattern
101 was compiled (the <i>tableptr</i> argument of <b>pcre_compile()</b>), you must
102 now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>,
103 because the value saved with the compiled pattern will obviously be nonsense. A
104 field in a <b>pcre_extra()</b> block is used to pass this data, as described in
105 the
106 <a href="pcreapi.html#extradata">section on matching a pattern</a>
107 in the
108 <a href="pcreapi.html"><b>pcreapi</b></a>
109 documentation.
110 </P>
111 <P>
112 If you did not provide custom character tables when the pattern was compiled,
113 the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to
114 use PCRE's internal tables. Thus, you do not need to take any special action at
115 run time in this case.
116 </P>
117 <P>
118 If you saved study data with the compiled pattern, you need to create your own
119 <b>pcre_extra</b> data block and set the <i>study_data</i> field to point to the
120 reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
121 <i>flags</i> field to indicate that study data is present. Then pass the
122 <b>pcre_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the
123 usual way.
124 </P>
126 <P>
127 In general, it is safest to recompile all saved patterns when you update to a
128 new PCRE release, though not all updates actually require this.
129 </P>
130 <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
131 <P>
132 Philip Hazel
133 <br>
134 University Computing Service
135 <br>
136 Cambridge CB2 3QH, England.
137 <br>
138 </P>
139 <br><a name="SEC6" href="#TOC1">REVISION</a><br>
140 <P>
141 Last updated: 17 November 2010
142 <br>
143 Copyright &copy; 1997-2010 University of Cambridge.
144 <br>
145 <p>
146 Return to the <a href="index.html">PCRE index page</a>.
147 </p>


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