regen

regen (regex engine) is a library for matching text with regular expressions written in C.
This is a one-man hobby project, there is no testing and bugs are regularly checked into main.
You probably shouldn’t use this in your own projects.

Syntax

regen supports the following operators and building blocks:

Symbol	Name	Example
\	Escape	\| matches | literally.
|	Alternator	a | b | c matches either a, b, or c.
(…)	Group	(a | b)(c | d) matches either a or b followed by either c or d.
[_, _]	Character Range	[a, z] matches any character from a to z. (Parser only)
{_, _}	Repetition Range	a{3, 5} matches sequences of 3-5 a’s. (Parser only)
?	Optional	a? matches a or nothing.
+	Multiple	a+ matches sequences of at least one a.
*	Any	a* matches any sequence of a’s.

abc* does not match repetitions of abc, but ab followed by any number of c’s. To match the former, use (abc)* instead.

Any whitespace in the regex is ignored.
To match whitespace, either escape it or use reserved keywords such as \n or \t.

Installation

To install, clone this repository and run make lib in the root of the project. It will generate lib/libregen.so that you can copy to whereever you need it.

Usage

To use regen you will need to link against libregen.so and also copy src/matcher.h to your own project. After that you can use it like this:

#include <stdlib.h>
#include <stdio.h>
#include "path/to/matcher.h"

int main(int argc, char** argv) {
    char* text = "Having a chat with a cat wearing a hat!";
    char* regex = "(c|h)+at!?";

    size_t matches_count = 0;
    Match* matches = match(text, regex, &matches_count);

    for (size_t idx = 0; idx < matches_count; idx++) {
        Match m = matches[idx];
        printf("Found \"%.*s\"\n", (int)m.length, text + m.offset);
    }

    free(matches);
    return 0;
}

When calling match you need to pass your text and regex as well as a size_t* which will contain the number of matches after the function ends. This way you can to iterate over the returned matches.

The return value of match is an array of structs containing offset and length, but no additional information about the text itself.
So don't touch the text until you have done everything you want with the matches!