NAME

regex_compile regex_free – Compile a regular expression from a pattern

SYNOPSIS

#include <rationl.h>
reg_t regex_compile(char* pattern);
void regex_free(reg_t re);

DESCRIPTION

regex_compile() takes a regular expression pattern and compiles it into a regular expression matching the pattern.

The value returned is a reg_t structure containing the folowing fields:

typedef struct reg_t
{


    Automaton* aut;


    char* pattern;
} regex_t;

aut This fields hold a compiled automaton that matches the pattern passed as argument to the compile function. This automaton will then be used by the other function to performs the operations on the automaton.

pattern This fields hold the pattern passed as argument.

REGULAR EXPRESSION FORMAT

Currently supported regular expression operators are :

? Corresponds to zero or one occurence of the element. For instance, the regular expression aa? will match a and aa but will not match aaa.

* Corresponds to zero, one or several the the precedent element. The regular expression a* matches an empty string, a, aaaa... but will not match ab.

+ Corresponds to at least one element. The regular expression a+ will match a, aa, aaaaaa... but will not match an empty string.

{n} Repeats the element n times. For instance the regular expression b{4} wil match only match bbbb.

{n,} Repeats at least the element n times. The regular expression b{4,} wil match bbbb, bbbbb... but will not match bb or bbb.

{n,p} Repeats between n and p times the element preceding the . The regular expression b{4,} wil match bbbb, bbbbb... but will not match bb or bbb.

a|b Matches expression a or b. For instance the regular expression a|b will match a and b but will not match ab. This operator as the lowest precedence meaning that aa|bb will match either aa or bb.

() When a pattern or an expression is put between parenthesis, it enforces precedence. For example the regular expression defined as (aa)? will match if aa occurs zero or one time.

[] This operator creates a group of caracters than can be matched. Consider the regular expression [abc]. This expression will match a, b or c. When a group is defined using - like in [A-Z] it will match all the caracters in the ASCII order contained between A and Z. To match all alphanumerical word you can use the folowing expression [A-Za-z0-9] that will match either a caracter between A and Z, a caracter between a and z or a number between 0 and 9.

\w This is equivalent to writing [A-Za-z0-9_]. Matches all alphanumerical words including and underscores.

\W This matches everything except all the caracters in \w

\d This is equivalent to writing [0-9]. Matches all numbers.

\D This matches everything except all the caracters in \d

\s Matches all blank characters (\t, \n, \r, \v) and spaces.

\S Matches everything that is not a blank character.

RETURN VALUE

regex_compiles() returns a element of the reg_t struct or NULL on failure to compile the regular expression.

This regular expression needs to be freed using the regex_free() function.