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Revision 128 - (show annotations)
Tue Mar 20 11:46:50 2007 UTC (13 years, 10 months ago) by ph10
File size: 9225 byte(s)
Make the use of dftables optional, and not the default. Further tidies to 
3 PCRE - Perl-compatible regular expressions
5 .rs
6 .sp
7 This document describes the optional features of PCRE that can be selected when
8 the library is compiled. They are all selected, or deselected, by providing
9 options to the \fBconfigure\fP script that is run before the \fBmake\fP
10 command. The complete list of options for \fBconfigure\fP (which includes the
11 standard ones such as the selection of the installation directory) can be
12 obtained by running
13 .sp
14 ./configure --help
15 .sp
16 The following sections include descriptions of options whose names begin with
17 --enable or --disable. These settings specify changes to the defaults for the
18 \fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
19 --enable and --disable always come in pairs, so the complementary option always
20 exists as well, but as it specifies the default, it is not described.
21 .
22 .SH "C++ SUPPORT"
23 .rs
24 .sp
25 By default, the \fBconfigure\fP script will search for a C++ compiler and C++
26 header files. If it finds them, it automatically builds the C++ wrapper library
27 for PCRE. You can disable this by adding
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29 --disable-cpp
30 .sp
31 to the \fBconfigure\fP command.
32 .
34 .rs
35 .sp
36 To build PCRE with support for UTF-8 character strings, add
37 .sp
38 --enable-utf8
39 .sp
40 to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
41 strings as UTF-8. As well as compiling PCRE with this option, you also have
42 have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
43 function.
44 .
46 .rs
47 .sp
48 UTF-8 support allows PCRE to process character values greater than 255 in the
49 strings that it handles. On its own, however, it does not provide any
50 facilities for accessing the properties of such characters. If you want to be
51 able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
52 character properties, you must add
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54 --enable-unicode-properties
55 .sp
56 to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
57 not explicitly requested it.
58 .P
59 Including Unicode property support adds around 30K of tables to the PCRE
60 library. Only the general category properties such as \fILu\fP and \fINd\fP are
61 supported. Details are given in the
62 .\" HREF
63 \fBpcrepattern\fP
64 .\"
65 documentation.
66 .
68 .rs
69 .sp
70 By default, PCRE interprets character 10 (linefeed, LF) as indicating the end
71 of a line. This is the normal newline character on Unix-like systems. You can
72 compile PCRE to use character 13 (carriage return, CR) instead, by adding
73 .sp
74 --enable-newline-is-cr
75 .sp
76 to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
77 which explicitly specifies linefeed as the newline character.
78 .sp
79 Alternatively, you can specify that line endings are to be indicated by the two
80 character sequence CRLF. If you want this, add
81 .sp
82 --enable-newline-is-crlf
83 .sp
84 to the \fBconfigure\fP command. There is a fourth option, specified by
85 .sp
86 --enable-newline-is-any
87 .sp
88 which causes PCRE to recognize any Unicode newline sequence.
89 .P
90 Whatever line ending convention is selected when PCRE is built can be
91 overridden when the library functions are called. At build time it is
92 conventional to use the standard for your operating system.
93 .
95 .rs
96 .sp
97 The PCRE building process uses \fBlibtool\fP to build both shared and static
98 Unix libraries by default. You can suppress one of these by adding one of
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100 --disable-shared
101 --disable-static
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103 to the \fBconfigure\fP command, as required.
104 .
106 .rs
107 .sp
108 When PCRE is called through the POSIX interface (see the
109 .\" HREF
110 \fBpcreposix\fP
111 .\"
112 documentation), additional working storage is required for holding the pointers
113 to capturing substrings, because PCRE requires three integers per substring,
114 whereas the POSIX interface provides only two. If the number of expected
115 substrings is small, the wrapper function uses space on the stack, because this
116 is faster than using \fBmalloc()\fP for each call. The default threshold above
117 which the stack is no longer used is 10; it can be changed by adding a setting
118 such as
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120 --with-posix-malloc-threshold=20
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122 to the \fBconfigure\fP command.
123 .
125 .rs
126 .sp
127 Within a compiled pattern, offset values are used to point from one part to
128 another (for example, from an opening parenthesis to an alternation
129 metacharacter). By default, two-byte values are used for these offsets, leading
130 to a maximum size for a compiled pattern of around 64K. This is sufficient to
131 handle all but the most gigantic patterns. Nevertheless, some people do want to
132 process enormous patterns, so it is possible to compile PCRE to use three-byte
133 or four-byte offsets by adding a setting such as
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135 --with-link-size=3
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137 to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
138 longer offsets slows down the operation of PCRE because it has to load
139 additional bytes when handling them.
140 .
142 .rs
143 .sp
144 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
145 by making recursive calls to an internal function called \fBmatch()\fP. In
146 environments where the size of the stack is limited, this can severely limit
147 PCRE's operation. (The Unix environment does not usually suffer from this
148 problem, but it may sometimes be necessary to increase the maximum stack size.
149 There is a discussion in the
150 .\" HREF
151 \fBpcrestack\fP
152 .\"
153 documentation.) An alternative approach to recursion that uses memory from the
154 heap to remember data, instead of using recursive function calls, has been
155 implemented to work round the problem of limited stack size. If you want to
156 build a version of PCRE that works this way, add
157 .sp
158 --disable-stack-for-recursion
159 .sp
160 to the \fBconfigure\fP command. With this configuration, PCRE will use the
161 \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
162 management functions. Separate functions are provided because the usage is very
163 predictable: the block sizes requested are always the same, and the blocks are
164 always freed in reverse order. A calling program might be able to implement
165 optimized functions that perform better than the standard \fBmalloc()\fP and
166 \fBfree()\fP functions. PCRE runs noticeably more slowly when built in this
167 way. This option affects only the \fBpcre_exec()\fP function; it is not
168 relevant for the the \fBpcre_dfa_exec()\fP function.
169 .
171 .rs
172 .sp
173 Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
174 (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
175 function. By controlling the maximum number of times this function may be
176 called during a single matching operation, a limit can be placed on the
177 resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
178 at run time, as described in the
179 .\" HREF
180 \fBpcreapi\fP
181 .\"
182 documentation. The default is 10 million, but this can be changed by adding a
183 setting such as
184 .sp
185 --with-match-limit=500000
186 .sp
187 to the \fBconfigure\fP command. This setting has no effect on the
188 \fBpcre_dfa_exec()\fP matching function.
189 .P
190 In some environments it is desirable to limit the depth of recursive calls of
191 \fBmatch()\fP more strictly than the total number of calls, in order to
192 restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
193 is specified) that is used. A second limit controls this; it defaults to the
194 value that is set for --with-match-limit, which imposes no additional
195 constraints. However, you can set a lower limit by adding, for example,
196 .sp
197 --with-match-limit-recursion=10000
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199 to the \fBconfigure\fP command. This value can also be overridden at run time.
200 .
202 .rs
203 .sp
204 PCRE uses fixed tables for processing characters whose code values are less
205 than 256. By default, PCRE is built with a set of tables that are distributed
206 in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
207 only. If you add
208 .sp
209 --enable-rebuild-chartables
210 .sp
211 to the \fBconfigure\fP command, the distributed tables are no longer used.
212 Instead, a program called \fBdftables\fP is compiled and run. This outputs the
213 source for new set of tables, created in the default locale of your C runtime
214 system. (This method of replacing the tables does not work if you are cross
215 compiling, because \fBdftables\fP is run on the local host. If you need to
216 create alternative tables when cross compiling, you will have to do so "by
217 hand".)
218 .
220 .rs
221 .sp
222 PCRE assumes by default that it will run in an environment where the character
223 code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
224 compiled to run in an EBCDIC environment by adding
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226 --enable-ebcdic
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228 to the \fBconfigure\fP command. This setting implies
229 --enable-rebuild-chartables.
230 .
231 .
232 .SH "SEE ALSO"
233 .rs
234 .sp
235 \fBpcreapi\fP(3), \fBpcre_config\fP(3).
236 .
237 .
239 .rs
240 .sp
241 .nf
242 Philip Hazel
243 University Computing Service
244 Cambridge CB2 3QH, England.
245 .fi
246 .
247 .
249 .rs
250 .sp
251 .nf
252 Last updated: 20 March 2007
253 Copyright (c) 1997-2007 University of Cambridge.
254 .fi


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