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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 </ul>
22 <P>
23 If you are running an application that uses a large number of regular
24 expression patterns, it may be useful to store them in a precompiled form
25 instead of having to compile them every time the application is run.
26 If you are not using any private character tables (see the
27 <a href="pcre_maketables.html"><b>pcre_maketables()</b></a>
28 documentation), this is relatively straightforward. If you are using private
29 tables, it is a little bit more complicated.
30 </P>
31 <P>
32 If you save compiled patterns to a file, you can copy them to a different host
33 and run them there. This works even if the new host has the opposite endianness
34 to the one on which the patterns were compiled. There may be a small
35 performance penalty, but it should be insignificant.
36 </P>
37 <br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
38 <P>
39 The value returned by <b>pcre_compile()</b> points to a single block of memory
40 that holds the compiled pattern and associated data. You can find the length of
41 this block in bytes by calling <b>pcre_fullinfo()</b> with an argument of
42 PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is
43 sample code that compiles a pattern and writes it to a file. It assumes that
44 the variable <i>fd</i> refers to a file that is open for output:
45 <pre>
46 int erroroffset, rc, size;
47 char *error;
48 pcre *re;
50 re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
51 if (re == NULL) { ... handle errors ... }
52 rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
53 if (rc &#60; 0) { ... handle errors ... }
54 rc = fwrite(re, 1, size, fd);
55 if (rc != size) { ... handle errors ... }
56 </pre>
57 In this example, the bytes that comprise the compiled pattern are copied
58 exactly. Note that this is binary data that may contain any of the 256 possible
59 byte values. On systems that make a distinction between binary and non-binary
60 data, be sure that the file is opened for binary output.
61 </P>
62 <P>
63 If you want to write more than one pattern to a file, you will have to devise a
64 way of separating them. For binary data, preceding each pattern with its length
65 is probably the most straightforward approach. Another possibility is to write
66 out the data in hexadecimal instead of binary, one pattern to a line.
67 </P>
68 <P>
69 Saving compiled patterns in a file is only one possible way of storing them for
70 later use. They could equally well be saved in a database, or in the memory of
71 some daemon process that passes them via sockets to the processes that want
72 them.
73 </P>
74 <P>
75 If the pattern has been studied, it is also possible to save the study data in
76 a similar way to the compiled pattern itself. When studying generates
77 additional information, <b>pcre_study()</b> returns a pointer to a
78 <b>pcre_extra</b> data block. Its format is defined in the
79 <a href="pcreapi.html#extradata">section on matching a pattern</a>
80 in the
81 <a href="pcreapi.html"><b>pcreapi</b></a>
82 documentation. The <i>study_data</i> field points to the binary study data, and
83 this is what you must save (not the <b>pcre_extra</b> block itself). The length
84 of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an
85 argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_study()</b> did
86 return a non-NULL value before trying to save the study data.
87 </P>
88 <br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
89 <P>
90 Re-using a precompiled pattern is straightforward. Having reloaded it into main
91 memory, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in
92 the usual way. This should work even on another host, and even if that host has
93 the opposite endianness to the one where the pattern was compiled.
94 </P>
95 <P>
96 However, if you passed a pointer to custom character tables when the pattern
97 was compiled (the <i>tableptr</i> argument of <b>pcre_compile()</b>), you must
98 now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>,
99 because the value saved with the compiled pattern will obviously be nonsense. A
100 field in a <b>pcre_extra()</b> block is used to pass this data, as described in
101 the
102 <a href="pcreapi.html#extradata">section on matching a pattern</a>
103 in the
104 <a href="pcreapi.html"><b>pcreapi</b></a>
105 documentation.
106 </P>
107 <P>
108 If you did not provide custom character tables when the pattern was compiled,
109 the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to
110 use PCRE's internal tables. Thus, you do not need to take any special action at
111 run time in this case.
112 </P>
113 <P>
114 If you saved study data with the compiled pattern, you need to create your own
115 <b>pcre_extra</b> data block and set the <i>study_data</i> field to point to the
116 reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
117 <i>flags</i> field to indicate that study data is present. Then pass the
118 <b>pcre_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the
119 usual way.
120 </P>
122 <P>
123 The layout of the control block that is at the start of the data that makes up
124 a compiled pattern was changed for release 5.0. If you have any saved patterns
125 that were compiled with previous releases (not a facility that was previously
126 advertised), you will have to recompile them for release 5.0. However, from now
127 on, it should be possible to make changes in a compabible manner.
128 </P>
129 <P>
130 Last updated: 28 February 2005
131 <br>
132 Copyright &copy; 1997-2005 University of Cambridge.
133 <p>
134 Return to the <a href="index.html">PCRE index page</a>.
135 </p>

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