Annotation of embedaddon/pcre/doc/html/pcreprecompile.html, revision 1.1.1.2
1.1 misho 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>
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
1.1.1.2 ! misho 32: just-in-time optimization feature, it is not possible to save and reload the
! 33: JIT data.
1.1 misho 34: </P>
35: <P>
36: If you save compiled patterns to a file, you can copy them to a different host
1.1.1.2 ! misho 37: and run them there. If the two hosts have different endianness (byte order),
! 38: you should run the <b>pcre[16]_pattern_to_host_byte_order()</b> function on the
! 39: new host before trying to match the pattern. The matching functions return
! 40: PCRE_ERROR_BADENDIANNESS if they detect a pattern with the wrong endianness.
! 41: </P>
! 42: <P>
! 43: Compiling regular expressions with one version of PCRE for use with a different
! 44: version is not guaranteed to work and may cause crashes, and saving and
! 45: restoring a compiled pattern loses any JIT optimization data.
1.1 misho 46: </P>
47: <br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
48: <P>
1.1.1.2 ! misho 49: The value returned by <b>pcre[16]_compile()</b> points to a single block of
! 50: memory that holds the compiled pattern and associated data. You can find the
! 51: length of this block in bytes by calling <b>pcre[16]_fullinfo()</b> with an
! 52: argument of PCRE_INFO_SIZE. You can then save the data in any appropriate
! 53: manner. Here is sample code for the 8-bit library that compiles a pattern and
! 54: writes it to a file. It assumes that the variable <i>fd</i> refers to a file
! 55: that is open for output:
1.1 misho 56: <pre>
57: int erroroffset, rc, size;
58: char *error;
59: pcre *re;
60:
61: re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
62: if (re == NULL) { ... handle errors ... }
63: rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
64: if (rc < 0) { ... handle errors ... }
65: rc = fwrite(re, 1, size, fd);
66: if (rc != size) { ... handle errors ... }
67: </pre>
68: In this example, the bytes that comprise the compiled pattern are copied
69: exactly. Note that this is binary data that may contain any of the 256 possible
70: byte values. On systems that make a distinction between binary and non-binary
71: data, be sure that the file is opened for binary output.
72: </P>
73: <P>
74: If you want to write more than one pattern to a file, you will have to devise a
75: way of separating them. For binary data, preceding each pattern with its length
76: is probably the most straightforward approach. Another possibility is to write
77: out the data in hexadecimal instead of binary, one pattern to a line.
78: </P>
79: <P>
80: Saving compiled patterns in a file is only one possible way of storing them for
81: later use. They could equally well be saved in a database, or in the memory of
82: some daemon process that passes them via sockets to the processes that want
83: them.
84: </P>
85: <P>
86: If the pattern has been studied, it is also possible to save the normal study
87: data in a similar way to the compiled pattern itself. However, if the
88: PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is created cannot
89: be saved because it is too dependent on the current environment. When studying
1.1.1.2 ! misho 90: generates additional information, <b>pcre[16]_study()</b> returns a pointer to a
! 91: <b>pcre[16]_extra</b> data block. Its format is defined in the
1.1 misho 92: <a href="pcreapi.html#extradata">section on matching a pattern</a>
93: in the
94: <a href="pcreapi.html"><b>pcreapi</b></a>
95: documentation. The <i>study_data</i> field points to the binary study data, and
1.1.1.2 ! misho 96: this is what you must save (not the <b>pcre[16]_extra</b> block itself). The
! 97: length of the study data can be obtained by calling <b>pcre[16]_fullinfo()</b>
! 98: with an argument of PCRE_INFO_STUDYSIZE. Remember to check that
! 99: <b>pcre[16]_study()</b> did return a non-NULL value before trying to save the
! 100: study data.
1.1 misho 101: </P>
102: <br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
103: <P>
104: Re-using a precompiled pattern is straightforward. Having reloaded it into main
1.1.1.2 ! misho 105: memory, called <b>pcre[16]_pattern_to_host_byte_order()</b> if necessary,
! 106: you pass its pointer to <b>pcre[16]_exec()</b> or <b>pcre[16]_dfa_exec()</b> in
! 107: the usual way.
1.1 misho 108: </P>
109: <P>
110: However, if you passed a pointer to custom character tables when the pattern
1.1.1.2 ! misho 111: was compiled (the <i>tableptr</i> argument of <b>pcre[16]_compile()</b>), you
! 112: must now pass a similar pointer to <b>pcre[16]_exec()</b> or
! 113: <b>pcre[16]_dfa_exec()</b>, because the value saved with the compiled pattern
! 114: will obviously be nonsense. A field in a <b>pcre[16]_extra()</b> block is used
! 115: to pass this data, as described in the
1.1 misho 116: <a href="pcreapi.html#extradata">section on matching a pattern</a>
117: in the
118: <a href="pcreapi.html"><b>pcreapi</b></a>
119: documentation.
120: </P>
121: <P>
122: If you did not provide custom character tables when the pattern was compiled,
1.1.1.2 ! misho 123: the pointer in the compiled pattern is NULL, which causes the matching
! 124: functions to use PCRE's internal tables. Thus, you do not need to take any
! 125: special action at run time in this case.
1.1 misho 126: </P>
127: <P>
128: If you saved study data with the compiled pattern, you need to create your own
1.1.1.2 ! misho 129: <b>pcre[16]_extra</b> data block and set the <i>study_data</i> field to point to the
1.1 misho 130: reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
131: <i>flags</i> field to indicate that study data is present. Then pass the
1.1.1.2 ! misho 132: <b>pcre[16]_extra</b> block to the matching function in the usual way. If the
! 133: pattern was studied for just-in-time optimization, that data cannot be saved,
! 134: and so is lost by a save/restore cycle.
1.1 misho 135: </P>
136: <br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
137: <P>
138: In general, it is safest to recompile all saved patterns when you update to a
139: new PCRE release, though not all updates actually require this.
140: </P>
141: <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
142: <P>
143: Philip Hazel
144: <br>
145: University Computing Service
146: <br>
147: Cambridge CB2 3QH, England.
148: <br>
149: </P>
150: <br><a name="SEC6" href="#TOC1">REVISION</a><br>
151: <P>
1.1.1.2 ! misho 152: Last updated: 10 January 2012
1.1 misho 153: <br>
1.1.1.2 ! misho 154: Copyright © 1997-2012 University of Cambridge.
1.1 misho 155: <br>
156: <p>
157: Return to the <a href="index.html">PCRE index page</a>.
158: </p>
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