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revision 99 by ph10, Tue Mar 6 12:27:42 2007 UTC revision 211 by ph10, Thu Aug 9 09:52:43 2007 UTC
# Line 47  and Line 47  and
47  .\" HREF  .\" HREF
48  \fBpcrecompat\fR  \fBpcrecompat\fR
49  .\"  .\"
50  pages.  pages. There is a syntax summary in the
51    .\" HREF
52    \fBpcresyntax\fR
53    .\"
54    page.
55  .P  .P
56  Some features of PCRE can be included, excluded, or changed when the library is  Some features of PCRE can be included, excluded, or changed when the library is
57  built. The  built. The
# Line 81  all the sections are concatenated, for e Line 85  all the sections are concatenated, for e
85  follows:  follows:
86  .sp  .sp
87    pcre              this document    pcre              this document
88      pcre-config       show PCRE installation configuration information
89    pcreapi           details of PCRE's native C API    pcreapi           details of PCRE's native C API
90    pcrebuild         options for building PCRE    pcrebuild         options for building PCRE
91    pcrecallout       details of the callout feature    pcrecallout       details of the callout feature
# Line 92  follows: Line 97  follows:
97  .\" JOIN  .\" JOIN
98    pcrepattern       syntax and semantics of supported    pcrepattern       syntax and semantics of supported
99                        regular expressions                        regular expressions
100      pcresyntax        quick syntax reference
101    pcreperform       discussion of performance issues    pcreperform       discussion of performance issues
102    pcreposix         the POSIX-compatible C API    pcreposix         the POSIX-compatible C API
103    pcreprecompile    details of saving and re-using precompiled patterns    pcreprecompile    details of saving and re-using precompiled patterns
# Line 120  distribution and the Line 126  distribution and the
126  documentation for details). In these cases the limit is substantially larger.  documentation for details). In these cases the limit is substantially larger.
127  However, the speed of execution is slower.  However, the speed of execution is slower.
128  .P  .P
129  All values in repeating quantifiers must be less than 65536. The maximum  All values in repeating quantifiers must be less than 65536.
 compiled length of subpattern with an explicit repeat count is 30000 bytes. The  
 maximum number of capturing subpatterns is 65535.  
130  .P  .P
131  There is no limit to the number of parenthesized subpatterns, but there can be  There is no limit to the number of parenthesized subpatterns, but there can be
132  no more than 65535 capturing subpatterns.  no more than 65535 capturing subpatterns.
# Line 140  issues, see the Line 144  issues, see the
144  \fBpcrestack\fP  \fBpcrestack\fP
145  .\"  .\"
146  documentation.  documentation.
147  .sp  .
148  .\" HTML <a name="utf8support"></a>  .\" HTML <a name="utf8support"></a>
149  .  .
150  .  .
# Line 178  documentation. Only the short names for Line 182  documentation. Only the short names for
182  \ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported.  \ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported.
183  Furthermore, in Perl, many properties may optionally be prefixed by "Is", for  Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
184  compatibility with Perl 5.6. PCRE does not support this.  compatibility with Perl 5.6. PCRE does not support this.
185  .P  .
186  The following comments apply when PCRE is running in UTF-8 mode:  .\" HTML <a name="utf8strings"></a>
187  .P  .
188  1. When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects  .SS "Validity of UTF-8 strings"
189  are checked for validity on entry to the relevant functions. If an invalid  .rs
190  UTF-8 string is passed, an error return is given. In some situations, you may  .sp
191  already know that your strings are valid, and therefore want to skip these  When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
192  checks in order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag  are (by default) checked for validity on entry to the relevant functions. From
193  at compile time or at run time, PCRE assumes that the pattern or subject it  release 7.3 of PCRE, the check is according the rules of RFC 3629, which are
194  is given (respectively) contains only valid UTF-8 codes. In this case, it does  themselves derived from the Unicode specification. Earlier releases of PCRE
195  not diagnose an invalid UTF-8 string. If you pass an invalid UTF-8 string to  followed the rules of RFC 2279, which allows the full range of 31-bit values (0
196  PCRE when PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  to 0x7FFFFFFF). The current check allows only values in the range U+0 to
197  may crash.  U+10FFFF, excluding U+D800 to U+DFFF.
198  .P  .P
199  2. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte  The excluded code points are the "Low Surrogate Area" of Unicode, of which the
200    Unicode Standard says this: "The Low Surrogate Area does not contain any
201    character assignments, consequently no character code charts or namelists are
202    provided for this area. Surrogates are reserved for use with UTF-16 and then
203    must be used in pairs." The code points that are encoded by UTF-16 pairs are
204    available as independent code points in the UTF-8 encoding. (In other words,
205    the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up
206    UTF-8.)
207    .P
208    If an invalid UTF-8 string is passed to PCRE, an error return
209    (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know that
210    your strings are valid, and therefore want to skip these checks in order to
211    improve performance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or
212    at run time, PCRE assumes that the pattern or subject it is given
213    (respectively) contains only valid UTF-8 codes. In this case, it does not
214    diagnose an invalid UTF-8 string.
215    .P
216    If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what
217    happens depends on why the string is invalid. If the string conforms to the
218    "old" definition of UTF-8 (RFC 2279), it is processed as a string of characters
219    in the range 0 to 0x7FFFFFFF. In other words, apart from the initial validity
220    test, PCRE (when in UTF-8 mode) handles strings according to the more liberal
221    rules of RFC 2279. However, if the string does not even conform to RFC 2279,
222    the result is undefined. Your program may crash.
223    .P
224    If you want to process strings of values in the full range 0 to 0x7FFFFFFF,
225    encoded in a UTF-8-like manner as per the old RFC, you can set
226    PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this
227    situation, you will have to apply your own validity check.
228    .
229    .SS "General comments about UTF-8 mode"
230    .rs
231    .sp
232    1. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte
233  UTF-8 character if the value is greater than 127.  UTF-8 character if the value is greater than 127.
234  .P  .P
235  3. Octal numbers up to \e777 are recognized, and match two-byte UTF-8  2. Octal numbers up to \e777 are recognized, and match two-byte UTF-8
236  characters for values greater than \e177.  characters for values greater than \e177.
237  .P  .P
238  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual  3. Repeat quantifiers apply to complete UTF-8 characters, not to individual
239  bytes, for example: \ex{100}{3}.  bytes, for example: \ex{100}{3}.
240  .P  .P
241  5. The dot metacharacter matches one UTF-8 character instead of a single byte.  4. The dot metacharacter matches one UTF-8 character instead of a single byte.
242  .P  .P
243  6. The escape sequence \eC can be used to match a single byte in UTF-8 mode,  5. The escape sequence \eC can be used to match a single byte in UTF-8 mode,
244  but its use can lead to some strange effects. This facility is not available in  but its use can lead to some strange effects. This facility is not available in
245  the alternative matching function, \fBpcre_dfa_exec()\fP.  the alternative matching function, \fBpcre_dfa_exec()\fP.
246  .P  .P
247  7. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly  6. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly
248  test characters of any code value, but the characters that PCRE recognizes as  test characters of any code value, but the characters that PCRE recognizes as
249  digits, spaces, or word characters remain the same set as before, all with  digits, spaces, or word characters remain the same set as before, all with
250  values less than 256. This remains true even when PCRE includes Unicode  values less than 256. This remains true even when PCRE includes Unicode
# Line 215  property support, because to do otherwis Line 252  property support, because to do otherwis
252  cases. If you really want to test for a wider sense of, say, "digit", you  cases. If you really want to test for a wider sense of, say, "digit", you
253  must use Unicode property tests such as \ep{Nd}.  must use Unicode property tests such as \ep{Nd}.
254  .P  .P
255  8. Similarly, characters that match the POSIX named character classes are all  7. Similarly, characters that match the POSIX named character classes are all
256  low-valued characters.  low-valued characters.
257  .P  .P
258    8. However, the Perl 5.10 horizontal and vertical whitespace matching escapes
259    (\eh, \eH, \ev, and \eV) do match all the appropriate Unicode characters.
260    .P
261  9. Case-insensitive matching applies only to characters whose values are less  9. Case-insensitive matching applies only to characters whose values are less
262  than 128, unless PCRE is built with Unicode property support. Even when Unicode  than 128, unless PCRE is built with Unicode property support. Even when Unicode
263  property support is available, PCRE still uses its own character tables when  property support is available, PCRE still uses its own character tables when
# Line 239  Cambridge CB2 3QH, England. Line 279  Cambridge CB2 3QH, England.
279  .fi  .fi
280  .P  .P
281  Putting an actual email address here seems to have been a spam magnet, so I've  Putting an actual email address here seems to have been a spam magnet, so I've
282  taken it away. If you want to email me, use my initial and surname, separated  taken it away. If you want to email me, use my two initials, followed by the
283  by a dot, at the domain ucs.cam.ac.uk.  two digits 10, at the domain cam.ac.uk.
284  .  .
285  .  .
286  .SH REVISION  .SH REVISION
287  .rs  .rs
288  .sp  .sp
289  .nf  .nf
290  Last updated: 06 March 2007  Last updated: 09 August 2007
291  Copyright (c) 1997-2007 University of Cambridge.  Copyright (c) 1997-2007 University of Cambridge.
292  .fi  .fi

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