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Load pcre-6.7 into code/trunk.
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 describe certain options whose names begin with --enable
17 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
28 .sp
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
53 .sp
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 90K of tables to the PCRE
60 library, approximately doubling its size. Only the general category properties
61 such as \fILu\fP and \fINd\fP are 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. Whatever line ending convention is selected
85 when PCRE is built can be overridden when the library functions are called. At
86 build time it is conventional to use the standard for your operating system.
87 .
89 .rs
90 .sp
91 The PCRE building process uses \fBlibtool\fP to build both shared and static
92 Unix libraries by default. You can suppress one of these by adding one of
93 .sp
94 --disable-shared
95 --disable-static
96 .sp
97 to the \fBconfigure\fP command, as required.
98 .
100 .rs
101 .sp
102 When PCRE is called through the POSIX interface (see the
103 .\" HREF
104 \fBpcreposix\fP
105 .\"
106 documentation), additional working storage is required for holding the pointers
107 to capturing substrings, because PCRE requires three integers per substring,
108 whereas the POSIX interface provides only two. If the number of expected
109 substrings is small, the wrapper function uses space on the stack, because this
110 is faster than using \fBmalloc()\fP for each call. The default threshold above
111 which the stack is no longer used is 10; it can be changed by adding a setting
112 such as
113 .sp
114 --with-posix-malloc-threshold=20
115 .sp
116 to the \fBconfigure\fP command.
117 .
119 .rs
120 .sp
121 Within a compiled pattern, offset values are used to point from one part to
122 another (for example, from an opening parenthesis to an alternation
123 metacharacter). By default, two-byte values are used for these offsets, leading
124 to a maximum size for a compiled pattern of around 64K. This is sufficient to
125 handle all but the most gigantic patterns. Nevertheless, some people do want to
126 process enormous patterns, so it is possible to compile PCRE to use three-byte
127 or four-byte offsets by adding a setting such as
128 .sp
129 --with-link-size=3
130 .sp
131 to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
132 longer offsets slows down the operation of PCRE because it has to load
133 additional bytes when handling them.
134 .P
135 If you build PCRE with an increased link size, test 2 (and test 5 if you are
136 using UTF-8) will fail. Part of the output of these tests is a representation
137 of the compiled pattern, and this changes with the link size.
138 .
140 .rs
141 .sp
142 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
143 by making recursive calls to an internal function called \fBmatch()\fP. In
144 environments where the size of the stack is limited, this can severely limit
145 PCRE's operation. (The Unix environment does not usually suffer from this
146 problem, but it may sometimes be necessary to increase the maximum stack size.
147 There is a discussion in the
148 .\" HREF
149 \fBpcrestack\fP
150 .\"
151 documentation.) An alternative approach to recursion that uses memory from the
152 heap to remember data, instead of using recursive function calls, has been
153 implemented to work round the problem of limited stack size. If you want to
154 build a version of PCRE that works this way, add
155 .sp
156 --disable-stack-for-recursion
157 .sp
158 to the \fBconfigure\fP command. With this configuration, PCRE will use the
159 \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
160 management functions. Separate functions are provided because the usage is very
161 predictable: the block sizes requested are always the same, and the blocks are
162 always freed in reverse order. A calling program might be able to implement
163 optimized functions that perform better than the standard \fBmalloc()\fP and
164 \fBfree()\fP functions. PCRE runs noticeably more slowly when built in this
165 way. This option affects only the \fBpcre_exec()\fP function; it is not
166 relevant for the the \fBpcre_dfa_exec()\fP function.
167 .
169 .rs
170 .sp
171 Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
172 (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
173 function. By controlling the maximum number of times this function may be
174 called during a single matching operation, a limit can be placed on the
175 resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
176 at run time, as described in the
177 .\" HREF
178 \fBpcreapi\fP
179 .\"
180 documentation. The default is 10 million, but this can be changed by adding a
181 setting such as
182 .sp
183 --with-match-limit=500000
184 .sp
185 to the \fBconfigure\fP command. This setting has no effect on the
186 \fBpcre_dfa_exec()\fP matching function.
187 .P
188 In some environments it is desirable to limit the depth of recursive calls of
189 \fBmatch()\fP more strictly than the total number of calls, in order to
190 restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
191 is specified) that is used. A second limit controls this; it defaults to the
192 value that is set for --with-match-limit, which imposes no additional
193 constraints. However, you can set a lower limit by adding, for example,
194 .sp
195 --with-match-limit-recursion=10000
196 .sp
197 to the \fBconfigure\fP command. This value can also be overridden at run time.
198 .
200 .rs
201 .sp
202 PCRE assumes by default that it will run in an environment where the character
203 code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
204 compiled to run in an EBCDIC environment by adding
205 .sp
206 --enable-ebcdic
207 .sp
208 to the \fBconfigure\fP command.
209 .P
210 .in 0
211 Last updated: 06 June 2006
212 .br
213 Copyright (c) 1997-2006 University of Cambridge.

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