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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 <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
   32 just-in-time optimization feature, it is not possible to save and reload the
   33 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. If the two hosts have different endianness (byte order),
   38 you should run the <b>pcre[16|32]_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.
   46 </P>
   47 <br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
   48 <P>
   49 The value returned by <b>pcre[16|32]_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|32]_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:
   56 <pre>
   57   int erroroffset, rc, size;
   58   char *error;
   59   pcre *re;
   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 &#60; 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
   90 generates additional information, <b>pcre[16|32]_study()</b> returns a pointer to a
   91 <b>pcre[16|32]_extra</b> data block. Its format is defined in the
   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
   96 this is what you must save (not the <b>pcre[16|32]_extra</b> block itself). The
   97 length of the study data can be obtained by calling <b>pcre[16|32]_fullinfo()</b>
   98 with an argument of PCRE_INFO_STUDYSIZE. Remember to check that
   99 <b>pcre[16|32]_study()</b> did return a non-NULL value before trying to save the
  100 study data.
  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
  105 memory, called <b>pcre[16|32]_pattern_to_host_byte_order()</b> if necessary, you
  106 pass its pointer to <b>pcre[16|32]_exec()</b> or <b>pcre[16|32]_dfa_exec()</b> in
  107 the usual way.
  108 </P>
  109 <P>
  110 However, if you passed a pointer to custom character tables when the pattern
  111 was compiled (the <i>tableptr</i> argument of <b>pcre[16|32]_compile()</b>), you
  112 must now pass a similar pointer to <b>pcre[16|32]_exec()</b> or
  113 <b>pcre[16|32]_dfa_exec()</b>, because the value saved with the compiled pattern
  114 will obviously be nonsense. A field in a <b>pcre[16|32]_extra()</b> block is used
  115 to pass this data, as described in the
  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 <b>Warning:</b> The tables that <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b> use
  123 must be the same as those that were used when the pattern was compiled. If this
  124 is not the case, the behaviour is undefined.
  125 </P>
  126 <P>
  127 If you did not provide custom character tables when the pattern was compiled,
  128 the pointer in the compiled pattern is NULL, which causes the matching
  129 functions to use PCRE's internal tables. Thus, you do not need to take any
  130 special action at run time in this case.
  131 </P>
  132 <P>
  133 If you saved study data with the compiled pattern, you need to create your own
  134 <b>pcre[16|32]_extra</b> data block and set the <i>study_data</i> field to point
  135 to the reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in
  136 the <i>flags</i> field to indicate that study data is present. Then pass the
  137 <b>pcre[16|32]_extra</b> block to the matching function in the usual way. If the
  138 pattern was studied for just-in-time optimization, that data cannot be saved,
  139 and so is lost by a save/restore cycle.
  140 </P>
  141 <br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
  142 <P>
  143 In general, it is safest to recompile all saved patterns when you update to a
  144 new PCRE release, though not all updates actually require this.
  145 </P>
  146 <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
  147 <P>
  148 Philip Hazel
  149 <br>
  150 University Computing Service
  151 <br>
  152 Cambridge CB2 3QH, England.
  153 <br>
  154 </P>
  155 <br><a name="SEC6" href="#TOC1">REVISION</a><br>
  156 <P>
  157 Last updated: 12 November 2013
  158 <br>
  159 Copyright &copy; 1997-2013 University of Cambridge.
  160 <br>
  161 <p>
  162 Return to the <a href="index.html">PCRE index page</a>.
  163 </p>