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:
| Syntax | Description |
|---|---|
* |
Zero or more of the preceding expression |
+ |
One or more of the preceding expression |
? |
Zero or one of the preceding expression |
| |
Alternation |
() |
Grouping |
a, b, c, ... |
Any single character |
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.