This repository implements a regex engine in C using Thompson's NFA algorithm. This algorithm prevents pathological backtracking, a common problem with most widely used regex implementations.

This implementation is also a header-only library.

To use the library, first include it in your C file.

// Optionally, you can define `CACHING` to allow
// the regex engine to cache transition states.
// This can improve performance in many cases.
#define CACHING

// Include the regex header file
#include "regex.hpp"

To use the regex engine, first create a regex object with the desired regex pattern. You can use std::cout to print out the compiled regex NFA. Use the match method to use the regex on a given content string.

int main() {
    // Compile a regex pattern
    Regex r("((ab)*|c) ");

    // Print out the compiled NFA
    std::cout << r << std::endl;

    // The content to match
    std::string content = "abc";

    // Check if the content matches the regex
    if (r.match(content)) {
        std::cout << "Matched!" << std::endl;
    } else {
        std::cout << "Not matched!" << std::endl;
    }

    return 0;
}

The regex engine supports the following syntax:

To build your program with the regex engine, simply add it to your include path and link against the C standard library.

g   -I path/to/regex-engine main.cpp -o main

To build with CMake, you can use a CMakeLists.txt file like the following:

cmake_minimum_required(VERSION 3.0)

# Create a new project
project(HelloWorld)

# Add an executable
add_executable(HelloWorld main.cpp)

include_directories(path/to/regex-engine)

Alternatively, you can use FetchContent to download the regex engine repository and include it in your project.

# Import the library from the git repo
include(FetchContent)

FetchContent_Declare(
  regex-engine
  GIT_REPOSITORY https://github.com/adam-mcdaniel/regex-engine
  GIT_TAG        main
)

FetchContent_MakeAvailable(regex-engine)

# Include the header only library
include_directories(${regex-engine_SOURCE_DIR})

This project is licensed under the MIT License - see the LICENSE file for details.