re2的c接口版本cre2的使用手册

Bertha 。 2022-05-21 09:21 202阅读 0赞

This is cre2.info, produced by makeinfo version 6.3 from cre2.texi.

This document describes version 0.3.4 of CRE2, a C language wrapper for  
the C++ library RE2: a fast, safe, thread-friendly alternative to  
backtracking regular expression engines like those used in PCRE, Perl,  
and Python.

The latest release can be downloaded from:

<https://bitbucket.org/marcomaggi/cre2/downloads>

development takes place at:

<http://github.com/marcomaggi/cre2>

and as backup at:

<https://bitbucket.org/marcomaggi/cre2>

Copyright (C) 2012, 2016 by Marco Maggi [http://github.com/marcomaggi][http_github.com_marcomaggi]  
Copyright (C) 2011 by Keegan McAllister [http://github.com/kmcallister/][http_github.com_kmcallister]

Portions of this document come from the source code of RE2 itself,  
see the file ‘LICENSE.re2’ for the license notice.

Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.3 or any later version published by the Free Software
     Foundation; with Invariant Sections being "GNU Free Documentation
     License" and "GNU General Public License", no Front-Cover Texts,
     and no Back-Cover Texts.  A copy of the license is included in the
     section entitled "GNU Free Documentation License".

INFO-DIR-SECTION Development  
START-INFO-DIR-ENTRY  
\* cre2: (cre2). C wrapper for RE2.  
END-INFO-DIR-ENTRY

File: cre2.info, Node: Top, Next: overview, Up: (dir)

C wrapper for RE2

--------------------

The latest release can be downloaded from:

<https://bitbucket.org/marcomaggi/cre2/downloads>

development takes place at:

<http://github.com/marcomaggi/cre2>

and as backup at:

<https://bitbucket.org/marcomaggi/cre2>

Portions of this document come from the source code of RE2 itself,  
see the file ‘LICENSE.re2’ for the license notice.

*  Menu:
 *  overview:: Overview of the package.
 *  version:: Version functions.
 *  regexps:: Precompiled regular expressions  
    construction.
 *  options:: Matching configuration.
 *  matching:: Matching regular expressions.
 *  other:: Other matching functions.
 *  tips:: Tips for using the regexp syntax.

Appendices

*  Package License:: Package license.
 *  Documentation License:: GNU Free Documentation License.
 *  references:: Bibliography and references.

Indexes

*  concept index:: An entry for each concept.
 *  function index:: An entry for each function.
 *  variable index:: An entry for each variable.
 *  type index:: An entry for each type.

File: cre2.info, Node: overview, Next: version, Prev: Top, Up: Top

1 Overview of the package

--------------------

CRE2 is a C language wrapper for the C++ library RE2: a fast, safe,  
thread-friendly alternative to backtracking regular expression engines  
like those used in PCRE, Perl, and Python. CRE2 is based on code by  
Keegan McAllister for the ‘haskell-re2’ binding:

<http://github.com/kmcallister/haskell-re2>

For the supported regular expressions syntax we should refer to the  
original documentation:

<https://github.com/google/re2/wiki/Syntax>

The C wrapper is meant to make it easier to interface RE2 with other  
languages. The exposed API allows searching for substrings of text  
matching regular expressions and reporting portions of text matching  
parenthetical subexpressions.

CRE2 installs the single header file ‘cre2.h’. All the function  
names in the API are prefixed with ‘cre2\_’; all the constant names are  
prefixed with ‘CRE2\_’; all the type names are prefixed with ‘cre2\_’ and  
suffixed with ‘\_t’.

When searching for the installed libraries with the GNU Autotools, we  
can use the following macros in ‘configure.ac’:

AC_CHECK_LIB([re2],[main],,
       [AC_MSG_FAILURE([test for RE2 library failed])])
    
     AC_CHECK_LIB([cre2],[cre2_version_string],,
       [AC_MSG_FAILURE([test for CRE2 library failed])])
     AC_CHECK_HEADERS([cre2.h],,
       [AC_MSG_ERROR([test for CRE2 header failed])])

notice that there is no need to check for the header file ‘re2/re2.h’.

It is customary for regular expression engines to provide methods to  
replace backslash sequences like ‘\\1’, ‘\\2’, … in a given string with  
portions of text that matched the first, second, … parenthetical  
subexpression; CRE2 does *not* provide such methods in its public API,  
because they require interacting with the storage mechanism in the  
client code. However, it is not difficult to implement such  
substitutions given the results of a regular expression matching  
operation.

Some functions and methods from RE2 requiring memory allocation  
handling are unofficially wrapped by CRE2 with unsafe code (execution  
will succeed when no memory allocation errors happen). These  
“problematic” functions are documented in the header file ‘cre2.h’ and,  
at present, are not considered part of the public API of CRE2.

It is sometimes useful to try a program in the original C++ to verify  
if a problem is caused by CRE2 or is in the original RE2 code; we may  
want to start by customising this program:

/* compile and run with:
    
        $ g++ -Wall -o proof proof.cpp -lre2 && ./proof
     */
    
     #include <re2/re2.h>
     #include <assert.h>
    
     static void try_match (RE2::Options& opt, const char * text);
    
     int
     main (int argc, const char *const argv[])
     {
       RE2::Options opt;
       opt.set_never_nl(true);
       try_match(opt, "abcdef");
       return 0;
     }
     void
     try_match (RE2::Options& opt, const char * text)
     {
       RE2 re("abcdef", opt);
       assert(re.ok());
       assert(RE2::FullMatch(text, re));
       //assert(RE2::PartialMatch(text, re));
     }

File: cre2.info, Node: version, Next: regexps, Prev: overview, Up: Top

2 Version functions

--------------------

The installed libraries follow version numbering as established by the  
GNU Autotools. For an explanation of interface numbers as managed by  
GNU Libtool \*Note interface: (libtool)Libtool versioning.

– Function: const char \* cre2\_version\_string (void)  
Return a pointer to a statically allocated ASCIIZ string  
representing the interface version number.

– Function: int cre2\_version\_interface\_current (void)  
Return an integer representing the library interface current  
number.

– Function: int cre2\_version\_interface\_revision (void)  
Return an integer representing the library interface current  
revision number.

– Function: int cre2\_version\_interface\_age (void)  
Return an integer representing the library interface current age.

File: cre2.info, Node: regexps, Next: options, Prev: version, Up: Top

3 Precompiled regular expressions construction

--------------------

Regular expression objects are built and finalised as follows:

cre2_regexp_t *   rex;
     cre2_options_t *  opt;
    
     opt = cre2_opt_new();
     if (opt) {
       cre2_opt_set_log_errors(opt, 0);
       rex = cre2_new("ciao", 4, opt);
       if (rex) {
         if (!cre2_error_code(rex))
           /* successfully built */
         else
           /* an error occurred while compiling rex */
         cre2_delete(rex);
       } else {
         /* rex memory allocation error */
       }
       cre2_opt_delete(opt);
     } else {
       /* opt memory allocation error */
     }

– Opaque Type: cre2\_regexp\_t  
Opaque type for regular expression objects; it is meant to be used  
to declare pointers to objects. Instances of this type can be used  
for any number of matching operations and are safe for concurrent  
use by multiple threads.

– Struct Typedef: cre2\_string\_t  
Simple data structure used to reference a portion of another  
string. It has the following fields:

'const char * data'
          Pointer to the first byte in the referenced substring.
    
     'int length'
          The number of bytes in the referenced substring.

– Enumeration Typedef: cre2\_error\_code\_t  
Enumeration type for error codes returned by ‘cre2\_error\_code()’.  
It contains the following symbols:

'CRE2_NO_ERROR'
          Defined as '0', represents a successful operation.
    
     'CRE2_ERROR_INTERNAL'
          Unexpected error.
    
     'CRE2_ERROR_BAD_ESCAPE'
          Bad escape sequence.
    
     'CRE2_ERROR_BAD_CHAR_CLASS'
          Bad character class.
    
     'CRE2_ERROR_BAD_CHAR_RANGE'
          Bad character class range.
    
     'CRE2_ERROR_MISSING_BRACKET'
          Missing closing ']'.
    
     'CRE2_ERROR_MISSING_PAREN'
          Missing closing ')'.
    
     'CRE2_ERROR_TRAILING_BACKSLASH'
          Trailing '\' at end of regexp.
    
     'CRE2_ERROR_REPEAT_ARGUMENT'
          Repeat argument missing, e.g.  '*'.
    
     'CRE2_ERROR_REPEAT_SIZE'
          Bad repetition argument.
    
     'CRE2_ERROR_REPEAT_OP'
          Bad repetition operator.
    
     'CRE2_ERROR_BAD_PERL_OP'
          Bad Perl operator.
    
     'CRE2_ERROR_BAD_UTF8'
          Invalid UTF-8 in regexp.
    
     'CRE2_ERROR_BAD_NAMED_CAPTURE'
          Bad named capture group.
    
     'CRE2_ERROR_PATTERN_TOO_LARGE'
          Pattern too large (compile failed).

– Function: cre2\_regexp\_t \* cre2\_new (const char \* PATTERN, int  
PATTERN\_LEN, const cre2\_options\_t \* OPT)  
Build and return a new regular expression object representing the  
PATTERN of length PATTERN\_LEN bytes; the object is configured with  
the options in OPT. If memory allocation fails: the return value  
is a ‘NULL’ pointer.

The options object OPT is duplicated in the internal state of the
     regular expression instance, so OPT can be safely mutated or
     finalised after this call.  If OPT is 'NULL': the regular
     expression object is built with the default set of options.

– Function: void cre2\_delete (cre2\_regexp\_t \* REX)  
Finalise a regular expression object releasing all the associated  
resources.

– Function: const char \* cre2\_pattern (const cre2\_regexp\_t \* REX)  
Whether REX is a successfully built regular expression object or  
not: return a pointer to the pattern string. The returned pointer  
is valid only while REX is alive: if ‘cre2\_delete()’ is applied to  
REX the pointer becomes invalid.

– Function: int cre2\_num\_capturing\_groups (const cre2\_regexp\_t \* REX)  
If REX is a successfully built regular expression object: return a  
non-negative integer representing the number of capturing groups  
(parenthetical subexpressions) in the pattern. If an error  
occurred while building REX: return ‘-1’.

– Function: int cre2\_find\_named\_capturing\_groups (const cre2\_regexp\_t  
\* REX, const char \* NAME)  
If REX is a successfully built regular expression object: return a  
non-negative integer representing the index of the named capturing  
group whose name is NAME. If an error occurred while building REX  
or the name is invalid: return ‘-1’.

const char *      pattern = "from (?P<S>.*) to (?P<D>.*)";
          cre2_options_t *  opt     = cre2_opt_new();
          cre2_regexp_t *   rex     = cre2_new(pattern, strlen(pattern),
                                               opt);
          {
            if (cre2_error_code(rex))
              { /* handle the error */ }
            int nmatch = cre2_num_capturing_groups(rex) + 1;
            cre2_string_t strings[nmatch];
            int e, SIndex, DIndex;
    
            const char * text = \
               "from Montreal, Canada to Lausanne, Switzerland";
            int text_len = strlen(text);
    
            e = cre2_match(rex, text, text_len, 0, text_len,
                           CRE2_UNANCHORED, strings, nmatch);
            if (0 == e)
              { /* handle the error */ }
    
            SIndex = cre2_find_named_capturing_groups(rex, "S");
            if (0 != strncmp("Montreal, Canada",
                             strings[SIndex].data, strings[SIndex].length))
              { /* handle the error */ }
    
            DIndex = cre2_find_named_capturing_groups(rex, "D");
            if (0 != strncmp("Lausanne, Switzerland",
                             strings[DIndex].data, strings[DIndex].length))
              { /* handle the error */ }
          }
          cre2_delete(rex);
          cre2_opt_delete(opt);

– Function: int cre2\_program\_size (const cre2\_regexp\_t \* REX)  
If REX is a successfully built regular expression object: return a  
non-negative integer representing the program size, a very  
approximate measure of a regexp’s “cost”; larger numbers are more  
expensive than smaller numbers. If an error occurred while  
building REX: return ‘-1’.

– Function: int cre2\_error\_code (const cre2\_regexp\_t \* REX)  
In case an error occurred while building REX: return an integer  
representing the associated error code. Return zero if no error  
occurred.

– Function: const char \* cre2\_error\_string (const cre2\_regexp\_t \* REX)  
If an error occurred while building REX: return a pointer to an  
ASCIIZ string representing the associated error message. The  
returned pointer is valid only while REX is alive: if  
‘cre2\_delete()’ is applied to REX the pointer becomes invalid.

If REX is a successfully built regular expression object: return a
     pointer to an empty string.
    
     The following code:
    
          cre2_regexp_t *   rex;
    
          rex = cre2_new("ci(ao", 5, NULL);
          {
            printf("error: code=%d, msg=\"%s\"\n",
                   cre2_error_code(rex),
                   cre2_error_string(rex));
          }
          cre2_delete(rex);
    
     prints:
    
          error: code=6, msg="missing ): ci(ao"

– Function: void cre2\_error\_arg (const cre2\_regexp\_t \* REX,  
cre2\_string\_t \* ARG)  
If an error occurred while building REX: fill the structure  
referenced by ARG with the interval of bytes representing the  
offending portion of the pattern.

If REX is a successfully built regular expression object: ARG
     references an empty string.
    
     The following code:
    
          cre2_regexp_t *   rex;
          cre2_string_t     S;
    
          rex = cre2_new("ci(ao", 5, NULL);
          {
            cre2_error_arg(rex, &S);
            printf("arg: len=%d, data=\"%s\"\n", S.length, S.data);
          }
          cre2_delete(rex);
    
     prints:
    
          arg: len=5 data="ci(ao"

File: cre2.info, Node: options, Next: matching, Prev: regexps, Up: Top

4 Matching configuration

--------------------

Compiled regular expressions can be configured, at construction-time,  
with a number of options collected in a ‘cre2\_options\_t’ object. Notice  
that, by default, when attempting to compile an invalid regular  
expression pattern, RE2 will print to ‘stderr’ an error message; usually  
we want to avoid this logging by disabling the associated option:

cre2_options_t *  opt;
    
     opt = cre2_opt_new();
     cre2_opt_set_log_errors(opt, 0);

– Opaque Typedef: cre2\_options\_t  
Type of opaque pointers to options objects. Any instance of this  
type can be used to configure any number of regular expression  
objects.

– Enumeration Typedef: cre2\_encoding\_t  
Enumeration type for constants selecting encoding. It contains the  
following values:

CRE2_UNKNOWN
          CRE2_UTF8
          CRE2_Latin1
    
     The value 'CRE2_UNKNOWN' should never be used: it exists only in
     case there is a mismatch between the definitions of RE2 and CRE2.

– Function: cre2\_options\_t \* cre2\_opt\_new (void)  
Allocate and return a new options object. If memory allocation  
fails: the return value is a ‘NULL’ pointer.

– Function: void cre2\_opt\_delete (cre2\_options\_t \* OPT)  
Finalise an options object releasing all the associated resources.  
Compiled regular expressions configured with this object are *not*  
affected by its destruction.

All the following functions are getters and setters for regular  
expression options; the FLAG argument to the setter must be false to  
disable the option and true to enable it; unless otherwise specified the  
‘int’ return value is true if the option is enabled and false if it is  
disabled.

– Function: cre2\_encoding\_t cre2\_opt\_encoding (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_encoding (cre2\_options\_t \* OPT,  
cre2\_encoding\_t ENC)  
By default, the regular expression pattern and input text are  
interpreted as UTF-8. CRE2\_Latin1 encoding causes them to be  
interpreted as Latin-1.

The getter returns 'CRE2_UNKNOWN' if the encoding value returned by
     RE2 is unknown.

– Function: int cre2\_opt\_posix\_syntax (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_posix\_syntax (cre2\_options\_t \* OPT, int  
FLAG)  
Restrict regexps to POSIX egrep syntax. Default is disabled.

– Function: int cre2\_opt\_longest\_match (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_longest\_match (cre2\_options\_t \* OPT, int  
FLAG)  
Search for longest match, not first match. Default is disabled.

– Function: int cre2\_opt\_log\_errors (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_log\_errors (cre2\_options\_t \* OPT, int  
FLAG)  
Log syntax and execution errors to ‘stderr’. Default is enabled.

– Function: int cre2\_opt\_literal (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_literal (cre2\_options\_t \* OPT, int FLAG)  
Interpret the pattern string as literal, not as regular expression.  
Default is disabled.

Setting this option is equivalent to quoting all the special
     characters defining a regular expression pattern:
    
          cre2_regexp_t *   rex;
          cre2_options_t *  opt;
          const char *      pattern = "(ciao) (hello)";
          const char *      text    = pattern;
          int               len     = strlen(pattern);
    
          opt = cre2_opt_new();
          cre2_opt_set_literal(opt, 1);
          rex = cre2_new(pattern, len, opt);
          {
            /* successful match */
            cre2_match(rex, text, len, 0, len,
                       CRE2_UNANCHORED, NULL, 0);
          }
          cre2_delete(rex);
          cre2_opt_delete(opt);

– Function: int cre2\_opt\_never\_nl (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_never\_nl (cre2\_options\_t \* OPT, int  
FLAG)  
Never match a newline character, even if it is in the regular  
expression pattern; default is disabled. Turning on this option  
allows us to attempt a partial match, against the beginning of a  
multiline text, without using subpatterns to exclude the newline in  
the regexp pattern.

* When set to true: matching always fails if the text or the
          regexp contains a newline.
    
        * When set to false: matching succeeds or fails taking normal
          account of newlines.
    
        * The option does *not* cause newlines to be skipped.

– Function: int cre2\_opt\_dot\_nl (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_dot\_nl (cre2\_options\_t \* OPT, int FLAG)  
The dot matches everything, including the new line; default is  
disabled.

– Function: int cre2\_opt\_never\_capture (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_never\_capture (cre2\_options\_t \* OPT, int  
FLAG)  
Parse all the parentheses as non-capturing; default is disabled.

– Function: int cre2\_opt\_case\_sensitive (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_case\_sensitive (cre2\_options\_t \* OPT,  
int FLAG)  
Match is case-sensitive; the regular expression pattern can  
override this setting with ‘(?i)’ unless configured in POSIX syntax  
mode. Default is enabled.

– Function: int cre2\_opt\_max\_mem (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_max\_mem (cre2\_options\_t \* OPT, int M)  
The max memory option controls how much memory can be used to hold  
the compiled form of the regular expression and its cached DFA  
graphs. These functions set and get such amount of memory. See  
the documentation of RE2 for details.

The following options are only consulted when POSIX syntax is  
enabled; when POSIX syntax is disabled: these features are always  
enabled and cannot be turned off.

– Function: int cre2\_opt\_perl\_classes (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_perl\_classes (cre2\_options\_t \* OPT, int  
FLAG)  
Allow Perl’s ‘\\d’, ‘\\s’, ‘\\w’, ‘\\D’, ‘\\S’, ‘\\W’. Default is  
disabled.

– Function: int cre2\_opt\_word\_boundary (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_word\_boundary (cre2\_options\_t \* OPT, int  
FLAG)  
Allow Perl’s ‘\\b’, ‘\\B’ (word boundary and not). Default is  
disabled.

– Function: int cre2\_opt\_one\_line (cre2\_options\_t \* OPT)  
– Function: void cre2\_opt\_set\_one\_line (cre2\_options\_t \* OPT, int  
FLAG)  
The patterns ‘^’ and ‘$’ only match at the beginning and end of the  
text. Default is disabled.

File: cre2.info, Node: matching, Next: other, Prev: options, Up: Top

5 Matching regular expressions

--------------------

Basic pattern matching goes as follows (with error checking omitted):

cre2_regexp_t *   rex;
     cre2_options_t *  opt;
     const char *      pattern = "(ciao) (hello)";
    
     opt = cre2_opt_new();
     cre2_opt_set_posix_syntax(opt, 1);
    
     rex = cre2_new(pattern, strlen(pattern), opt);
     {
       const char *   text     = "ciao hello";
       int            text_len = strlen(text);
       int            nmatch   = 3;
       cre2_string_t  match[nmatch];
    
       cre2_match(rex, text, text_len, 0, text_len, CRE2_UNANCHORED,
                  match, nmatch);
    
       /* prints: full match: ciao hello */
       printf("full match: ");
       fwrite(match[0].data, match[0].length, 1, stdout);
       printf("\n");
    
       /* prints: first group: ciao */
       printf("first group: ");
       fwrite(match[1].data, match[1].length, 1, stdout);
       printf("\n");
    
       /* prints: second group: hello */
       printf("second group: ");
       fwrite(match[2].data, match[2].length, 1, stdout);
       printf("\n");
     }
     cre2_delete(rex);
     cre2_opt_delete(opt);

– Enumeration Typedef: cre2\_anchor\_t  
Enumeration type for the anchor point of matching operations. It  
contains the following constants:

CRE2_UNANCHORED
          CRE2_ANCHOR_START
          CRE2_ANCHOR_BOTH

– Function: int cre2\_match (const cre2\_regexp\_t \* REX, const char \*  
TEXT, int TEXT\_LEN, int START\_POS, int END\_POS, cre2\_anchor\_t  
ANCHOR, cre2\_string\_t \* MATCH, int NMATCH)  
Match a substring of the text referenced by TEXT and holding  
TEXT\_LEN bytes against the regular expression object REX. Return  
true if the text matched, false otherwise.

The zero-based indices START_POS (inclusive) and END_POS
     (exclusive) select the substring of TEXT to be examined.  ANCHOR
     selects the anchor point for the matching operation.
    
     Data about the matching groups is stored in the array MATCH, which
     must have at least NMATCH entries; the referenced substrings are
     portions of the TEXT buffer.  If we are only interested in
     verifying if the text matches or not (ignoring the matching
     portions of text): we can use 'NULL' as MATCH argument and 0 as
     NMATCH argument.
    
     The first element of MATCH (index 0) references the full portion of
     the substring of TEXT matching the pattern; the second element of
     MATCH (index 1) references the portion of text matching the first
     parenthetical subexpression, the third element of MATCH (index 2)
     references the portion of text matching the second parenthetical
     subexpression; and so on.

– Function: int cre2\_easy\_match (const char \* PATTERN, int  
PATTERN\_LEN, const char \* TEXT, int TEXT\_LEN, cre2\_string\_t \*  
MATCH, int NMATCH)  
Like ‘cre2\_match()’ but the pattern is specified as string PATTERN  
holding PATTERN\_LEN bytes. Also the text is fully matched without  
anchoring.

If the text matches the pattern: the return value is 1.  If the
     text does not match the pattern: the return value is 0.  If the
     pattern is invalid: the return value is 2.

– Struct Typedef: cre2\_range\_t  
Structure type used to represent a substring of the text to be  
matched as starting and ending indices. It has the following  
fields:

'long start'
          Inclusive start byte index.
    
     'long past'
          Exclusive end byte index.

– Function: void cre2\_strings\_to\_ranges (const char \* TEXT,  
cre2\_range\_t \* RANGES, cre2\_string\_t \* STRINGS, int NMATCH)  
Given an array of STRINGS with NMATCH elements being the result of  
matching TEXT against a regular expression: fill the array of  
RANGES with the index intervals in the TEXT buffer representing the  
same results.

File: cre2.info, Node: other, Next: tips, Prev: matching, Up: Top

6 Other matching functions

--------------------

The following functions match a buffer of text against a regular  
expression, allowing the extraction of portions of text matching  
parenthetical subexpressions. All of them show the following behaviour:

*  If the text matches the pattern: the return value is 1; if the text  
    does not match the pattern: the return value is 0.
 *  If the pattern is invalid: the return value is 0; there is no way  
    to distinguish this case from the case of text not matching other  
    than looking at what RE2 prints to ‘stderr’.
 *  It is impossible to turn off logging of error messages to ‘stderr’  
    when the specification of the regular expression is invalid.
 *  Data about the matching groups is stored in the array MATCH, which  
    must have at least NMATCH slots; the referenced substrings are  
    portions of the TEXT buffer.
 *  The array MATCH can have a number of slots between zero (included)  
    and the number of parenthetical subexpressions in PATTERN  
    (excluded); if NMATCH is greater than the number of parenthetical  
    subexpressions: the return value is 0.
 *  If we are only interested in verifying if the text matches the  
    pattern or not: we can use ‘NULL’ as MATCH argument and 0 as NMATCH  
    argument.
 *  The first slot of MATCH (index 0) references the portion of text  
    matching the first parenthetical subexpression; the second slot of  
    MATCH (index 1) references the portion of text matching the second  
    parenthetical subexpression; and so on.

see the documentation of each function for the differences.

The following example is a successful match:

const char *   pattern = "ci.*ut";
     const char *   text    = "ciao salut";
     cre2_string_t  input   = {
       .data   = text,
       .length = strlen(text)
     };
     int            result;
     result = cre2_full_match(pattern, &input, NULL, 0);
    
     result => 1

the following example is a successful match in which the parenthetical  
subexpression is ignored:

const char *   pattern = "(ciao) salut";
     const char *   text    = "ciao salut";
     cre2_string_t  input   = {
       .data   = text,
       .length = strlen(text)
     };
     int            result;
     result = cre2_full_match(pattern, &input, NULL, 0);
    
     result => 1

the following example is a successful match in which the portion of text  
matching the parenthetical subexpression is reported:

const char *   pattern = "(ciao) salut";
     const char *   text    = "ciao salut";
     cre2_string_t  input   = {
       .data   = text,
       .length = strlen(text)
     };
     int            nmatch  = 1;
     cre2_string_t  match[nmatch];
     int            result;
     result = cre2_full_match(pattern, &input, match, nmatch);
    
     result => 1
     strncmp(text, input.data, input.length)         => 0
     strncmp("ciao", match[0].data, match[0].length) => 0

– Function: int cre2\_full\_match (const char \* PATTERN, const  
cre2\_string\_t \* TEXT, cre2\_string\_t \* MATCH, int NMATCH)  
– Function: int cre2\_full\_match\_re (cre2\_regexp\_t \* REX, const  
cre2\_string\_t \* TEXT, cre2\_string\_t \* MATCH, int NMATCH)  
Match the zero-terminated string PATTERN or the precompiled regular  
expression REX against the full buffer TEXT.

For example: the text 'abcdef' matches the pattern 'abcdef'
     according to this function, but neither the pattern 'abc' nor the
     pattern 'def' will match.

– Function: int cre2\_partial\_match (const char \* PATTERN, const  
cre2\_string\_t \* TEXT, cre2\_string\_t \* MATCH, int NMATCH)  
– Function: int cre2\_partial\_match\_re (cre2\_regexp\_t \* REX, const  
cre2\_string\_t \* TEXT, cre2\_string\_t \* MATCH, int NMATCH)  
Match the zero-terminated string PATTERN or the precompiled regular  
expression REX against the buffer TEXT, resulting in success if a  
substring of TEXT matches; these functions behave like the full  
match ones, but the matching text does not need to be anchored to  
the beginning and end.

For example: the text 'abcDEFghi' matches the pattern 'DEF'
     according to this function.

– Function: int cre2\_consume (const char \* PATTERN, cre2\_string\_t \*  
TEXT, cre2\_string\_t \* MATCH, int NMATCH)  
– Function: int cre2\_consume\_re (cre2\_regexp\_t \* REX, cre2\_string\_t \*  
TEXT, cre2\_string\_t \* MATCH, int NMATCH)  
Match the zero-terminated string PATTERN or the precompiled regular  
expression REX against the buffer TEXT, resulting in success if the  
prefix of TEXT matches. The data structure referenced by TEXT is  
mutated to reference text right after the last byte that matched  
the pattern.

For example: the text 'abcDEF' matches the pattern 'abc' according
     to this function; after the call TEXT will reference the text
     'DEF'.

– Function: int cre2\_find\_and\_consume (const char \* PATTERN,  
cre2\_string\_t \* TEXT, cre2\_string\_t \* MATCH, int NMATCH)  
– Function: int cre2\_find\_and\_consume\_re (cre2\_regexp\_t \* REX,  
cre2\_string\_t \* TEXT, cre2\_string\_t \* MATCH, int NMATCH)  
Match the zero-terminated string PATTERN or the precompiled regular  
expression REX against the buffer TEXT, resulting in success if,  
after skipping a non-matching prefix in TEXT, a substring of TEXT  
matches. The data structure referenced by TEXT is mutated to  
reference text right after the last byte that matched the pattern.

For example: the text 'abcDEFghi' matches the pattern 'DEF'
     according to this function; the prefix 'abc' is skipped; after the
     call TEXT will reference the text 'ghi'.

File: cre2.info, Node: tips, Next: Package License, Prev: other, Up: Top

7 Tips for using the regexp syntax

--------------------

*  Menu:
 *  tips dot:: Matching newlines with the  
    ‘.’ subpattern.

File: cre2.info, Node: tips dot, Up: tips

# 7.1 Matching newlines with the ‘.’ subpattern #

By default the dot subpattern ‘.’ matches any character but newlines; to  
enable newline matching we have to enable the ‘s’ flag using the special  
subpattern ‘(?)’ or ‘(?:)’, where ‘’ is a  
sequence of characters, one character for each flag, and ‘’ is a  
regexp subpattern. Notice that the parentheses in ‘(?:)’ are  
non-capturing.

So let’s consider the text ‘ciao\\nhello’:

*  The regexp ‘ciao.hello’ does *not* match because ‘s’ is disabled.
 *  The regexp ‘(?s)ciao.hello’ matches because the subpattern ‘(?s)’  
    has enabled flag ‘s’ for the rest of the pattern, including the  
    dot.
 *  The regexp ‘ciao(?s).hello’ matches because the subpattern ‘(?s)’  
    has enabled flag ‘s’ for the rest of the pattern, including the  
    dot.
 *  The regexp ‘ciao(?s:.)hello’ matches because the subpattern  
    ‘(?s:.)’ has enabled flag ‘s’ for the subpattern ‘.’ which is the  
    dot.

File: cre2.info, Node: Package License, Next: Documentation License, Prev: tips, Up: Top

Appendix A Package license

--------------------

Copyright (C) 2012, 2016 Marco Maggi [http://github.com/marcomaggi][http_github.com_marcomaggi]  
Copyright (C) 2011 Keegan McAllister [http://github.com/kmcallister/][http_github.com_kmcallister]  
All rights reserved.

Redistribution and use in source and binary forms, with or without  
modification, are permitted provided that the following conditions are  
met:

1.  Redistributions of source code must retain the above copyright  
    notice, this list of conditions and the following disclaimer.
2.  Redistributions in binary form must reproduce the above copyright  
    notice, this list of conditions and the following disclaimer in the  
    documentation and/or other materials provided with the  
    distribution.
3.  Neither the name of the author nor the names of his contributors  
    may be used to endorse or promote products derived from this  
    software without specific prior written permission.
    
    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS  
    “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT  
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A  
    PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR  
    CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,  
    EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,  
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR  
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF  
    LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING  
    NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS  
    SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

File: cre2.info, Node: Documentation License, Next: references, Prev: Package License, Up: Top

Appendix B GNU Free Documentation License

--------------------

Version 1.3, 3 November 2008
    
     Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     <http://fsf.org/>
    
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

1.  PREAMBLE
    
    The purpose of this License is to make a manual, textbook, or other  
    functional and useful document “free” in the sense of freedom: to  
    assure everyone the effective freedom to copy and redistribute it,  
    with or without modifying it, either commercially or  
    noncommercially. Secondarily, this License preserves for the  
    author and publisher a way to get credit for their work, while not  
    being considered responsible for modifications made by others.
    
    This License is a kind of “copyleft”, which means that derivative  
    works of the document must themselves be free in the same sense.  
    It complements the GNU General Public License, which is a copyleft  
    license designed for free software.
    
    We have designed this License in order to use it for manuals for  
    free software, because free software needs free documentation: a  
    free program should come with manuals providing the same freedoms  
    that the software does. But this License is not limited to  
    software manuals; it can be used for any textual work, regardless  
    of subject matter or whether it is published as a printed book. We  
    recommend this License principally for works whose purpose is  
    instruction or reference.
2.  APPLICABILITY AND DEFINITIONS
    
    This License applies to any manual or other work, in any medium,  
    that contains a notice placed by the copyright holder saying it can  
    be distributed under the terms of this License. Such a notice  
    grants a world-wide, royalty-free license, unlimited in duration,  
    to use that work under the conditions stated herein. The  
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    of the public is a licensee, and is addressed as “you”. You accept  
    the license if you copy, modify or distribute the work in a way  
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    A “Modified Version” of the Document means any work containing the  
    Document or a portion of it, either copied verbatim, or with  
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    A “Secondary Section” is a named appendix or a front-matter section  
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    The “Invariant Sections” are certain Secondary Sections whose  
    titles are designated, as being those of Invariant Sections, in the  
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    If a section does not fit the above definition of Secondary then it  
    is not allowed to be designated as Invariant. The Document may  
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    The “Cover Texts” are certain short passages of text that are  
    listed, as Front-Cover Texts or Back-Cover Texts, in the notice  
    that says that the Document is released under this License. A  
    Front-Cover Text may be at most 5 words, and a Back-Cover Text may  
    be at most 25 words.
    
    A “Transparent” copy of the Document means a machine-readable copy,  
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    the DTD and/or processing tools are not generally available, and  
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    The “Title Page” means, for a printed book, the title page itself,  
    plus such following pages as are needed to hold, legibly, the  
    material this License requires to appear in the title page. For  
    works in formats which do not have any title page as such, “Title  
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    work’s title, preceding the beginning of the body of the text.
    
    The “publisher” means any person or entity that distributes copies  
    of the Document to the public.
    
    A section “Entitled XYZ” means a named subunit of the Document  
    whose title either is precisely XYZ or contains XYZ in parentheses  
    following text that translates XYZ in another language. (Here XYZ  
    stands for a specific section name mentioned below, such as  
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    To “Preserve the Title” of such a section when you modify the  
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    to this definition.
    
    The Document may include Warranty Disclaimers next to the notice  
    which states that this License applies to the Document. These  
    Warranty Disclaimers are considered to be included by reference in  
    this License, but only as regards disclaiming warranties: any other  
    implication that these Warranty Disclaimers may have is void and  
    has no effect on the meaning of this License.
3.  VERBATIM COPYING
    
    You may copy and distribute the Document in any medium, either  
    commercially or noncommercially, provided that this License, the  
    copyright notices, and the license notice saying this License  
    applies to the Document are reproduced in all copies, and that you  
    add no other conditions whatsoever to those of this License. You  
    may not use technical measures to obstruct or control the reading  
    or further copying of the copies you make or distribute. However,  
    you may accept compensation in exchange for copies. If you  
    distribute a large enough number of copies you must also follow the  
    conditions in section 3.
    
    You may also lend copies, under the same conditions stated above,  
    and you may publicly display copies.
4.  COPYING IN QUANTITY
    
    If you publish printed copies (or copies in media that commonly  
    have printed covers) of the Document, numbering more than 100, and  
    the Document’s license notice requires Cover Texts, you must  
    enclose the copies in covers that carry, clearly and legibly, all  
    these Cover Texts: Front-Cover Texts on the front cover, and  
    Back-Cover Texts on the back cover. Both covers must also clearly  
    and legibly identify you as the publisher of these copies. The  
    front cover must present the full title with all words of the title  
    equally prominent and visible. You may add other material on the  
    covers in addition. Copying with changes limited to the covers, as  
    long as they preserve the title of the Document and satisfy these  
    conditions, can be treated as verbatim copying in other respects.
    
    If the required texts for either cover are too voluminous to fit  
    legibly, you should put the first ones listed (as many as fit  
    reasonably) on the actual cover, and continue the rest onto  
    adjacent pages.
    
    If you publish or distribute Opaque copies of the Document  
    numbering more than 100, you must either include a machine-readable  
    Transparent copy along with each Opaque copy, or state in or with  
    each Opaque copy a computer-network location from which the general  
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    reasonably prudent steps, when you begin distribution of Opaque  
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    year after the last time you distribute an Opaque copy (directly or  
    through your agents or retailers) of that edition to the public.
    
    It is requested, but not required, that you contact the authors of  
    the Document well before redistributing any large number of copies,  
    to give them a chance to provide you with an updated version of the  
    Document.
5.  MODIFICATIONS
    
    You may copy and distribute a Modified Version of the Document  
    under the conditions of sections 2 and 3 above, provided that you  
    release the Modified Version under precisely this License, with the  
    Modified Version filling the role of the Document, thus licensing  
    distribution and modification of the Modified Version to whoever  
    possesses a copy of it. In addition, you must do these things in  
    the Modified Version:
    
    A. Use in the Title Page (and on the covers, if any) a title  
    distinct from that of the Document, and from those of previous  
    versions (which should, if there were any, be listed in the  
    History section of the Document). You may use the same title  
    as a previous version if the original publisher of that  
    version gives permission.
    
    B. List on the Title Page, as authors, one or more persons or  
    entities responsible for authorship of the modifications in  
    the Modified Version, together with at least five of the  
    principal authors of the Document (all of its principal  
    authors, if it has fewer than five), unless they release you  
    from this requirement.
    
    C. State on the Title page the name of the publisher of the  
    Modified Version, as the publisher.
    
    D. Preserve all the copyright notices of the Document.
    
    E. Add an appropriate copyright notice for your modifications  
    adjacent to the other copyright notices.
    
    F. Include, immediately after the copyright notices, a license  
    notice giving the public permission to use the Modified  
    Version under the terms of this License, in the form shown in  
    the Addendum below.
    
    G. Preserve in that license notice the full lists of Invariant  
    Sections and required Cover Texts given in the Document’s  
    license notice.
    
    H. Include an unaltered copy of this License.
    
    I. Preserve the section Entitled “History”, Preserve its Title,  
    and add to it an item stating at least the title, year, new  
    authors, and publisher of the Modified Version as given on the  
    Title Page. If there is no section Entitled “History” in the  
    Document, create one stating the title, year, authors, and  
    publisher of the Document as given on its Title Page, then add  
    an item describing the Modified Version as stated in the  
    previous sentence.
    
    J. Preserve the network location, if any, given in the Document  
    for public access to a Transparent copy of the Document, and  
    likewise the network locations given in the Document for  
    previous versions it was based on. These may be placed in the  
    “History” section. You may omit a network location for a work  
    that was published at least four years before the Document  
    itself, or if the original publisher of the version it refers  
    to gives permission.
    
    K. For any section Entitled “Acknowledgements” or “Dedications”,  
    Preserve the Title of the section, and preserve in the section  
    all the substance and tone of each of the contributor  
    acknowledgements and/or dedications given therein.
    
    L. Preserve all the Invariant Sections of the Document, unaltered  
    in their text and in their titles. Section numbers or the  
    equivalent are not considered part of the section titles.
    
    M. Delete any section Entitled “Endorsements”. Such a section  
    may not be included in the Modified Version.
    
    N. Do not retitle any existing section to be Entitled  
    “Endorsements” or to conflict in title with any Invariant  
    Section.
    
    O. Preserve any Warranty Disclaimers.
    
    If the Modified Version includes new front-matter sections or  
    appendices that qualify as Secondary Sections and contain no  
    material copied from the Document, you may at your option designate  
    some or all of these sections as invariant. To do this, add their  
    titles to the list of Invariant Sections in the Modified Version’s  
    license notice. These titles must be distinct from any other  
    section titles.
    
    You may add a section Entitled “Endorsements”, provided it contains  
    nothing but endorsements of your Modified Version by various  
    parties–for example, statements of peer review or that the text  
    has been approved by an organization as the authoritative  
    definition of a standard.
    
    You may add a passage of up to five words as a Front-Cover Text,  
    and a passage of up to 25 words as a Back-Cover Text, to the end of  
    the list of Cover Texts in the Modified Version. Only one passage  
    of Front-Cover Text and one of Back-Cover Text may be added by (or  
    through arrangements made by) any one entity. If the Document  
    already includes a cover text for the same cover, previously added  
    by you or by arrangement made by the same entity you are acting on  
    behalf of, you may not add another; but you may replace the old  
    one, on explicit permission from the previous publisher that added  
    the old one.
    
    The author(s) and publisher(s) of the Document do not by this  
    License give permission to use their names for publicity for or to  
    assert or imply endorsement of any Modified Version.
6.  COMBINING DOCUMENTS
    
    You may combine the Document with other documents released under  
    this License, under the terms defined in section 4 above for  
    modified versions, provided that you include in the combination all  
    of the Invariant Sections of all of the original documents,  
    unmodified, and list them all as Invariant Sections of your  
    combined work in its license notice, and that you preserve all  
    their Warranty Disclaimers.
    
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    multiple identical Invariant Sections may be replaced with a single  
    copy. If there are multiple Invariant Sections with the same name  
    but different contents, make the title of each such section unique  
    by adding at the end of it, in parentheses, the name of the  
    original author or publisher of that section if known, or else a  
    unique number. Make the same adjustment to the section titles in  
    the list of Invariant Sections in the license notice of the  
    combined work.
    
    In the combination, you must combine any sections Entitled  
    “History” in the various original documents, forming one section  
    Entitled “History”; likewise combine any sections Entitled  
    “Acknowledgements”, and any sections Entitled “Dedications”. You  
    must delete all sections Entitled “Endorsements.”
7.  COLLECTIONS OF DOCUMENTS
    
    You may make a collection consisting of the Document and other  
    documents released under this License, and replace the individual  
    copies of this License in the various documents with a single copy  
    that is included in the collection, provided that you follow the  
    rules of this License for verbatim copying of each of the documents  
    in all other respects.
    
    You may extract a single document from such a collection, and  
    distribute it individually under this License, provided you insert  
    a copy of this License into the extracted document, and follow this  
    License in all other respects regarding verbatim copying of that  
    document.
8.  AGGREGATION WITH INDEPENDENT WORKS
    
    A compilation of the Document or its derivatives with other  
    separate and independent documents or works, in or on a volume of a  
    storage or distribution medium, is called an “aggregate” if the  
    copyright resulting from the compilation is not used to limit the  
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    If the Cover Text requirement of section 3 is applicable to these  
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9.  TRANSLATION
    
    Translation is considered a kind of modification, so you may  
    distribute translations of the Document under the terms of section
    
    1.  Replacing Invariant Sections with translations requires special  
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        disagreement between the translation and the original version of  
        this License or a notice or disclaimer, the original version will  
        prevail.
        
        If a section in the Document is Entitled “Acknowledgements”,  
        “Dedications”, or “History”, the requirement (section 4) to  
        Preserve its Title (section 1) will typically require changing the  
        actual title.
10. TERMINATION
    
    You may not copy, modify, sublicense, or distribute the Document  
    except as expressly provided under this License. Any attempt  
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    and will automatically terminate your rights under this License.
    
    However, if you cease all violation of this License, then your  
    license from a particular copyright holder is reinstated (a)  
    provisionally, unless and until the copyright holder explicitly and  
    finally terminates your license, and (b) permanently, if the  
    copyright holder fails to notify you of the violation by some  
    reasonable means prior to 60 days after the cessation.
    
    Moreover, your license from a particular copyright holder is  
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    violation by some reasonable means, this is the first time you have  
    received notice of violation of this License (for any work) from  
    that copyright holder, and you cure the violation prior to 30 days  
    after your receipt of the notice.
    
    Termination of your rights under this section does not terminate  
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    permanently reinstated, receipt of a copy of some or all of the  
    same material does not give you any rights to use it.
11. FUTURE REVISIONS OF THIS LICENSE
    
    The Free Software Foundation may publish new, revised versions of  
    the GNU Free Documentation License from time to time. Such new  
    versions will be similar in spirit to the present version, but may  
    differ in detail to address new problems or concerns. See  
    [http://www.gnu.org/copyleft/][http_www.gnu.org_copyleft].
    
    Each version of the License is given a distinguishing version  
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    version of this License “or any later version” applies to it, you  
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    Software Foundation. If the Document specifies that a proxy can  
    decide which future versions of this License can be used, that  
    proxy’s public statement of acceptance of a version permanently  
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12. RELICENSING
    
    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any  
    World Wide Web server that publishes copyrightable works and also  
    provides prominent facilities for anybody to edit those works. A  
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    A “Massive Multiauthor Collaboration” (or “MMC”) contained in the  
    site means any set of copyrightable works thus published on the MMC  
    site.
    
    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0  
    license published by Creative Commons Corporation, a not-for-profit  
    corporation with a principal place of business in San Francisco,  
    California, as well as future copyleft versions of that license  
    published by that same organization.
    
    “Incorporate” means to publish or republish a Document, in whole or  
    in part, as part of another Document.
    
    An MMC is “eligible for relicensing” if it is licensed under this  
    License, and if all works that were first published under this  
    License somewhere other than this MMC, and subsequently  
    incorporated in whole or in part into the MMC, (1) had no cover  
    texts or invariant sections, and (2) were thus incorporated prior  
    to November 1, 2008.
    
    The operator of an MMC Site may republish an MMC contained in the  
    site under CC-BY-SA on the same site at any time before August 1,  
    2009, provided the MMC is eligible for relicensing.

# ADDENDUM: How to use this License for your documents #

To use this License in a document you have written, include a copy of  
the License in the document and put the following copyright and license  
notices just after the title page:

Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover  
Texts, replace the “with…Texts.” line with this:

with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

If you have Invariant Sections without Cover Texts, or some other  
combination of the three, merge those two alternatives to suit the  
situation.

If your document contains nontrivial examples of program code, we  
recommend releasing these examples in parallel under your choice of free  
software license, such as the GNU General Public License, to permit  
their use in free software.

File: cre2.info, Node: references, Next: concept index, Prev: Documentation License, Up: Top

Appendix C Bibliography and references

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File: cre2.info, Node: concept index, Next: function index, Prev: references, Up: Top

Appendix D An entry for each concept

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[http_github.com_marcomaggi]: http://github.com/marcomaggi
[http_github.com_kmcallister]: http://github.com/kmcallister/
[http_www.gnu.org_copyleft]: http://www.gnu.org/copyleft/