159 lines
7.0 KiB
HTML
159 lines
7.0 KiB
HTML
<html>
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<head>
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<title>pcreprecompile specification</title>
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</head>
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<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
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<h1>pcreprecompile man page</h1>
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<p>
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Return to the <a href="index.html">PCRE index page</a>.
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</p>
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<p>
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This page is part of the PCRE HTML documentation. It was generated automatically
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from the original man page. If there is any nonsense in it, please consult the
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man page, in case the conversion went wrong.
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<br>
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<ul>
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<li><a name="TOC1" href="#SEC1">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a>
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<li><a name="TOC2" href="#SEC2">SAVING A COMPILED PATTERN</a>
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<li><a name="TOC3" href="#SEC3">RE-USING A PRECOMPILED PATTERN</a>
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<li><a name="TOC4" href="#SEC4">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a>
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<li><a name="TOC5" href="#SEC5">AUTHOR</a>
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<li><a name="TOC6" href="#SEC6">REVISION</a>
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</ul>
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<br><a name="SEC1" href="#TOC1">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a><br>
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<P>
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If you are running an application that uses a large number of regular
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expression patterns, it may be useful to store them in a precompiled form
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instead of having to compile them every time the application is run.
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If you are not using any private character tables (see the
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<a href="pcre_maketables.html"><b>pcre_maketables()</b></a>
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documentation), this is relatively straightforward. If you are using private
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tables, it is a little bit more complicated. However, if you are using the
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just-in-time optimization feature, it is not possible to save and reload the
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JIT data.
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</P>
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<P>
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If you save compiled patterns to a file, you can copy them to a different host
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and run them there. If the two hosts have different endianness (byte order),
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you should run the <b>pcre[16|32]_pattern_to_host_byte_order()</b> function on the
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new host before trying to match the pattern. The matching functions return
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PCRE_ERROR_BADENDIANNESS if they detect a pattern with the wrong endianness.
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</P>
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<P>
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Compiling regular expressions with one version of PCRE for use with a different
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version is not guaranteed to work and may cause crashes, and saving and
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restoring a compiled pattern loses any JIT optimization data.
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</P>
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<br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
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<P>
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The value returned by <b>pcre[16|32]_compile()</b> points to a single block of
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memory that holds the compiled pattern and associated data. You can find the
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length of this block in bytes by calling <b>pcre[16|32]_fullinfo()</b> with an
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argument of PCRE_INFO_SIZE. You can then save the data in any appropriate
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manner. Here is sample code for the 8-bit library that compiles a pattern and
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writes it to a file. It assumes that the variable <i>fd</i> refers to a file
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that is open for output:
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<pre>
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int erroroffset, rc, size;
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char *error;
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pcre *re;
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re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
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if (re == NULL) { ... handle errors ... }
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rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
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if (rc < 0) { ... handle errors ... }
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rc = fwrite(re, 1, size, fd);
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if (rc != size) { ... handle errors ... }
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</pre>
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In this example, the bytes that comprise the compiled pattern are copied
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exactly. Note that this is binary data that may contain any of the 256 possible
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byte values. On systems that make a distinction between binary and non-binary
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data, be sure that the file is opened for binary output.
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</P>
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<P>
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If you want to write more than one pattern to a file, you will have to devise a
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way of separating them. For binary data, preceding each pattern with its length
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is probably the most straightforward approach. Another possibility is to write
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out the data in hexadecimal instead of binary, one pattern to a line.
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</P>
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<P>
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Saving compiled patterns in a file is only one possible way of storing them for
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later use. They could equally well be saved in a database, or in the memory of
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some daemon process that passes them via sockets to the processes that want
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them.
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</P>
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<P>
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If the pattern has been studied, it is also possible to save the normal study
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data in a similar way to the compiled pattern itself. However, if the
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PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is created cannot
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be saved because it is too dependent on the current environment. When studying
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generates additional information, <b>pcre[16|32]_study()</b> returns a pointer to a
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<b>pcre[16|32]_extra</b> data block. Its format is defined in the
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<a href="pcreapi.html#extradata">section on matching a pattern</a>
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in the
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<a href="pcreapi.html"><b>pcreapi</b></a>
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documentation. The <i>study_data</i> field points to the binary study data, and
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this is what you must save (not the <b>pcre[16|32]_extra</b> block itself). The
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length of the study data can be obtained by calling <b>pcre[16|32]_fullinfo()</b>
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with an argument of PCRE_INFO_STUDYSIZE. Remember to check that
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<b>pcre[16|32]_study()</b> did return a non-NULL value before trying to save the
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study data.
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</P>
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<br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
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<P>
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Re-using a precompiled pattern is straightforward. Having reloaded it into main
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memory, called <b>pcre[16|32]_pattern_to_host_byte_order()</b> if necessary,
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you pass its pointer to <b>pcre[16|32]_exec()</b> or <b>pcre[16|32]_dfa_exec()</b> in
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the usual way.
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</P>
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<P>
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However, if you passed a pointer to custom character tables when the pattern
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was compiled (the <i>tableptr</i> argument of <b>pcre[16|32]_compile()</b>), you
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must now pass a similar pointer to <b>pcre[16|32]_exec()</b> or
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<b>pcre[16|32]_dfa_exec()</b>, because the value saved with the compiled pattern
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will obviously be nonsense. A field in a <b>pcre[16|32]_extra()</b> block is used
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to pass this data, as described in the
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<a href="pcreapi.html#extradata">section on matching a pattern</a>
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in the
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<a href="pcreapi.html"><b>pcreapi</b></a>
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documentation.
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</P>
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<P>
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If you did not provide custom character tables when the pattern was compiled,
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the pointer in the compiled pattern is NULL, which causes the matching
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functions to use PCRE's internal tables. Thus, you do not need to take any
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special action at run time in this case.
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</P>
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<P>
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If you saved study data with the compiled pattern, you need to create your own
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<b>pcre[16|32]_extra</b> data block and set the <i>study_data</i> field to point to the
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reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
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<i>flags</i> field to indicate that study data is present. Then pass the
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<b>pcre[16|32]_extra</b> block to the matching function in the usual way. If the
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pattern was studied for just-in-time optimization, that data cannot be saved,
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and so is lost by a save/restore cycle.
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</P>
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<br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
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<P>
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In general, it is safest to recompile all saved patterns when you update to a
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new PCRE release, though not all updates actually require this.
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</P>
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<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
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<P>
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Philip Hazel
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<br>
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University Computing Service
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<br>
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Cambridge CB2 3QH, England.
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<br>
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</P>
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<br><a name="SEC6" href="#TOC1">REVISION</a><br>
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<P>
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Last updated: 24 June 2012
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<br>
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Copyright © 1997-2012 University of Cambridge.
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<br>
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<p>
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Return to the <a href="index.html">PCRE index page</a>.
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</p>
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