C语言中的正则

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C语言中的正则

C++中的正则

boost中的正则

1.四个重要函数及一些定义

REGEX(3)     Linux Programmer's Manual                                                        
NAME         regcomp, regexec, regerror, regfree - POSIX regex functions

SYNOPSIS
#include <sys/types.h>
#include <regex.h>
int regcomp(regex_t *preg, const char *regex, int cflags);
int regexec(const regex_t *preg, const char *string, size_t nmatch,regmatch_t pmatch[], int eflags);
size_t regerror(int errcode, const regex_t *preg, char *errbuf,size_t errbuf_size);
void regfree(regex_t *preg);

1.1 regcomp-编译正则表达式

int regcomp(regex_t *preg, const char *regex, int cflags);
POSIX regex compiling
regcomp() is used to compile a regular expression into a form that is suitable 
for subsequent regexec() searches.

regcomp()  is supplied with preg, a pointer to a pattern buffer storage area; 
regex, a pointer to the null-terminated string and cflags, flags used to determine 
the type of compilation.

All regular expression searching must be done via a compiled pattern buffer, thus regexec() must always be supplied with the address of a regcomp() initialized 
pattern buffer.

cflags may be the bitwise-or of one or more of the following:
REG_EXTENDED
       Use POSIX Extended Regular Expression syntax when interpreting regex.  
       If not set, POSIX Basic Regular Expression syntax is used.

REG_ICASE
        Do not differentiate case.  Subsequent regexec() searches using this 
        pattern buffer will be case insensitive.

REG_NOSUB
        Do  not  report  position  of matches.  The nmatch and pmatch arguments 
        to regexec() are ignored if the pattern buffer supplied was compiled
        with this flag set.

REG_NEWLINE
        Match-any-character operators don't match a newline.
        A nonmatching list ([^...])  not containing a newline does not match a newline.
        Match-beginning-of-line operator (^) matches the empty string immediately after a
 newline, regardless of whether eflags, the execution flags of regexec(), contains REG_NOTBOL.
        Match-end-of-line operator ($) matches the empty string immediately before a 
newline, regardless of whether eflags contains REG_NOTEOL.


RETURN VALUE
regcomp() returns zero for a successful compilation or an error code for failure.

1.2 regexec-匹配正则表达式

POSIX regex matching
int regexec(const regex_t *preg, const char *string, size_t nmatch,regmatch_t pmatch[], int eflags);


regexec()  is  used to match a null-terminated string against the precompiled pattern 
buffer, preg, nmatch and pmatch are used to provide information regarding the location 
of any matches.  eflags may be the bitwise-or of one or both of REG_NOTBOL and 
REG_NOTEOL which cause changes in matching behavior described below.

REG_NOTBOL
The  match-beginning-of-line operator always fails to match (but see the compilation 
flag REG_NEWLINE above) This flag may be used when different portions of a string are
passed to regexec() and the beginning of the string should not be interpreted as the 
beginning of the line.

REG_NOTEOL
The match-end-of-line operator always fails to match (but see the compilation flag
REG_NEWLINE above)


RETURN VALUE
regexec() returns zero for a successful match or REG_NOMATCH for failure.

ERRORS
The following errors can be returned by regcomp():
REG_BADBR     Invalid use of back reference operator.
REG_BADPAT    Invalid use of pattern operators such as group or list.
REG_BADRPT    Invalid use of repetition operators such as using '*' as 
              the first character.
REG_EBRACE    Un-matched brace interval operators.
REG_EBRACK    Un-matched bracket list operators.
REG_ECOLLATE  Invalid collating element.
REG_ECTYPE    Unknown character class name.
REG_EEND      Nonspecific error.  This is not defined by POSIX.2.
REG_EESCAPE   Trailing backslash.
REG_EPAREN    Un-matched parenthesis group operators.
REG_ERANGE    Invalid use of the range operator, e.g., the ending point of the range 
              occurs prior to the starting point.
REG_ESIZE     Compiled regular expression requires a pattern buffer larger than 64Kb.
              This is not defined by POSIX.2.
REG_ESPACE    The regex routines ran out of memory.
REG_ESUBREG   Invalid back reference to a subexpression.

1.3 regerror-翻译正则匹配过程中的错误信息

POSIX error reporting
regerror() is used to turn the error codes that can be returned by both regcomp() and
regexec() into error message strings.

regerror() is passed the error code, errcode, the pattern buffer, preg, a pointer to 
a character string buffer, errbuf, and the size of the  string buffer,  errbuf_size.   
It  returns  the  size  of  the  errbuf  required  to contain the null-terminated 
error message string.  If both errbuf and errbuf_size are nonzero, errbuf is filled 
in with the first errbuf_size - 1 characters of the error message and a terminating 
null byte ('\0').

1.4 regfree-释放正则匹配过程中的资源

POSIX pattern buffer freeing
Supplying regfree() with a precompiled pattern buffer, preg will free the memory 
allocated to the pattern buffer by  the  compiling  process,  regcomp().

1.5 regmatch_t结构体

The regmatch_t structure which is the type of pmatch is defined in <regex.h>.
typedef struct 
{
  regoff_t rm_so;
  regoff_t rm_eo;
} regmatch_t;

Each  rm_so  element  that  is not -1 indicates the start offset of the next largest 
substring match within the string.  The relative rm_eo element indicates the end 
offset of the match, which is the offset of the first character after the matching 
text.


typedef int regoff_t;