ViewVC logotype

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

Parent Directory Parent Directory | Revision Log Revision Log

Revision 111 - (show annotations)
Thu Mar 8 16:53:09 2007 UTC (14 years, 2 months ago) by ph10
File MIME type: text/html
File size: 6910 byte(s)
Error occurred while calculating annotation data.
Create the PrepareRelease script to process the documentation and create the 
.generic files for distribution, also to remove trailing spaces. Update a lot 
more of the build-time documentation. Arrange for PrepareRelease and its 
sub-scripts to be distributed.
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.
38 </P>
39 <br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
40 <P>
41 The value returned by <b>pcre_compile()</b> points to a single block of memory
42 that holds the compiled pattern and associated data. You can find the length of
43 this block in bytes by calling <b>pcre_fullinfo()</b> with an argument of
44 PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is
45 sample code that compiles a pattern and writes it to a file. It assumes that
46 the variable <i>fd</i> refers to a file that is open for output:
47 <pre>
48 int erroroffset, rc, size;
49 char *error;
50 pcre *re;
52 re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
53 if (re == NULL) { ... handle errors ... }
54 rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
55 if (rc &#60; 0) { ... handle errors ... }
56 rc = fwrite(re, 1, size, fd);
57 if (rc != size) { ... handle errors ... }
58 </pre>
59 In this example, the bytes that comprise the compiled pattern are copied
60 exactly. Note that this is binary data that may contain any of the 256 possible
61 byte values. On systems that make a distinction between binary and non-binary
62 data, be sure that the file is opened for binary output.
63 </P>
64 <P>
65 If you want to write more than one pattern to a file, you will have to devise a
66 way of separating them. For binary data, preceding each pattern with its length
67 is probably the most straightforward approach. Another possibility is to write
68 out the data in hexadecimal instead of binary, one pattern to a line.
69 </P>
70 <P>
71 Saving compiled patterns in a file is only one possible way of storing them for
72 later use. They could equally well be saved in a database, or in the memory of
73 some daemon process that passes them via sockets to the processes that want
74 them.
75 </P>
76 <P>
77 If the pattern has been studied, it is also possible to save the study data in
78 a similar way to the compiled pattern itself. When studying generates
79 additional information, <b>pcre_study()</b> returns a pointer to a
80 <b>pcre_extra</b> data block. Its format is defined in the
81 <a href="pcreapi.html#extradata">section on matching a pattern</a>
82 in the
83 <a href="pcreapi.html"><b>pcreapi</b></a>
84 documentation. The <i>study_data</i> field points to the binary study data, and
85 this is what you must save (not the <b>pcre_extra</b> block itself). The length
86 of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an
87 argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_study()</b> did
88 return a non-NULL value before trying to save the study data.
89 </P>
90 <br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
91 <P>
92 Re-using a precompiled pattern is straightforward. Having reloaded it into main
93 memory, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in
94 the usual way. This should work even on another host, and even if that host has
95 the opposite endianness to the one where the pattern was compiled.
96 </P>
97 <P>
98 However, if you passed a pointer to custom character tables when the pattern
99 was compiled (the <i>tableptr</i> argument of <b>pcre_compile()</b>), you must
100 now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>,
101 because the value saved with the compiled pattern will obviously be nonsense. A
102 field in a <b>pcre_extra()</b> block is used to pass this data, as described in
103 the
104 <a href="pcreapi.html#extradata">section on matching a pattern</a>
105 in the
106 <a href="pcreapi.html"><b>pcreapi</b></a>
107 documentation.
108 </P>
109 <P>
110 If you did not provide custom character tables when the pattern was compiled,
111 the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to
112 use PCRE's internal tables. Thus, you do not need to take any special action at
113 run time in this case.
114 </P>
115 <P>
116 If you saved study data with the compiled pattern, you need to create your own
117 <b>pcre_extra</b> data block and set the <i>study_data</i> field to point to the
118 reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
119 <i>flags</i> field to indicate that study data is present. Then pass the
120 <b>pcre_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the
121 usual way.
122 </P>
124 <P>
125 The layout of the control block that is at the start of the data that makes up
126 a compiled pattern was changed for release 5.0. If you have any saved patterns
127 that were compiled with previous releases (not a facility that was previously
128 advertised), you will have to recompile them for release 5.0 and above.
129 </P>
130 <P>
131 If you have any saved patterns in UTF-8 mode that use \p or \P that were
132 compiled with any release up to and including 6.4, you will have to recompile
133 them for release 6.5 and above.
134 </P>
135 <P>
136 All saved patterns from earlier releases must be recompiled for release 7.0 or
137 higher, because there was an internal reorganization at that release.
138 </P>
139 <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
140 <P>
141 Philip Hazel
142 <br>
143 University Computing Service
144 <br>
145 Cambridge CB2 3QH, England.
146 <br>
147 </P>
148 <br><a name="SEC6" href="#TOC1">REVISION</a><br>
149 <P>
150 Last updated: 06 March 2007
151 <br>
152 Copyright &copy; 1997-2007 University of Cambridge.
153 <br>
154 <p>
155 Return to the <a href="index.html">PCRE index page</a>.
156 </p>


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

  ViewVC Help
Powered by ViewVC 1.1.5