ViewVC logotype

Contents of /code/trunk/doc/html/pcreprecompile.html

Parent Directory Parent Directory | Revision Log Revision Log

Revision 691 - (show annotations)
Sun Sep 11 14:31:21 2011 UTC (9 years, 8 months ago) by ph10
File MIME type: text/html
File size: 7049 byte(s)
Final source and document tidies for 8.20-RC1.
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. 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;
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 &#60; 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>
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 &copy; 1997-2011 University of Cambridge.
150 <br>
151 <p>
152 Return to the <a href="index.html">PCRE index page</a>.
153 </p>


Name Value
svn:eol-style native
svn:keywords "Author Date Id Revision Url"

  ViewVC Help
Powered by ViewVC 1.1.5