Lua in C++

A simple bridge between Lua's API and C++.

This repository is still work in progress but starts to be useable. You can find classes to use Lua's API in C++ and use it to script things into your C++ programs.

This has been tested with C++ 20 on g++, Lua 5.4 and Ubuntu 22.04.

Installation

Clone this repository and compile the static or shared library (see this) like this:

make libluaincpp.a
make libluaincpp.so

Then you're free to use and link it with your program.

How to use

Here is a a Lua file and a C++ file showing you some of the features that this library does, you can find these files in the example folder:

function greets(name)
    print("[Lua] Hello "..name)
end

function my_sin_int(x)
    print("[Lua] "..math.sin(x))
end

function is_true(b)
    print("[Lua] ", b == true)
end

function my_sin_float(x)
    print("[Lua] "..math.sin(x))
end

function both_sin(x1, x2)
    my_sin_float(x1)
    my_sin_int(x2)
end

function all(name, b, f, i)
    greets(name)
    is_true(b)
    my_sin_float(f)
    my_sin_int(i)
    return 1234
end

function add_test()
    print("[Lua] "..mymath.add(1, 2))
end

#include <string.h>
#include "LuaInCpp.hpp"

// To call a C++ function in Lua, you have to use the Lua API
// Here's an example:
int add(lua_State *l)
{
    int n = lua_gettop(l); // get the number of arguments

    if (n != 2) {
        lua_pushliteral(l, "bad number of arguments");
        lua_error(l);
    }

    int a = lua_tointeger(l, 1); // get first argument
    int b = lua_tointeger(l, 2); // get second arument

    std::cout << "[C++] " << a << " + " << b << std::endl;
    lua_pushinteger(l, a + b); // the return value
    return 1; // number of argument returned
}

int main()
{
    Lua l;
    l.openLibs();

    l.add("add", &add, "mymath");

    if (l.loadFile("test.lua")) {
        LuaFunction<void(const char *)> greets(l, "greets");
        char *s = strdup("Frodo"); // works with not const too
        greets(s);

        LuaFunction<void(int)> my_sin(l, "my_sin_int");
        long a = 0; // works with long too
        my_sin(a);

        LuaFunction<void(double)> my_sin_float(l, "my_sin_float");
        my_sin_float(2.3);

        LuaFunction<void(bool)> is_true(l, "is_true");
        is_true(false);

        LuaFunction<void(double, int)> both_sin(l, "both_sin");
        both_sin(2.3, 4);

        std::cout << std::endl;

        LuaFunction<int(const char *, bool, double, int)> all(l, "all");
        int b = all(s, false, 2.3, 4);
        std::cout << b << std::endl;

        l.call("main");
    }
}

Compile and run like this:

make test
./test

And the output will be:

[Lua] Hello Frodo
[Lua] 0.0
[Lua] 0.74570521217672
[Lua] 	false
[Lua] 0.74570521217672
[Lua] -0.75680249530793

[Lua] Hello Frodo
[Lua] 	false
[Lua] 0.74570521217672
[Lua] -0.75680249530793
1234

[C++] 1 + 2
[Lua] 3

What is currently being done ?

This library is able to do:

Injecting C++ values, functions and tables in a lua instance
Call thoses C++ functions in lua
Call lua functions in C++ (cannot call functions with multiple return values for now)

Known issues

Why can't I compile it in a shared library ?

To compile this project into a shared library, you must also have a shared library of lua itself. For that, you can go here to download the source code of your favorite version of lua and tweak the Makefile in the src folder to create a liblua.so and place it next to the liblua.a already installed on your system

Then you can have this library in a shared format like that:

make libluaincpp.so

Other issues

If you have any idea on how to solve these problems or you want to contribute, please open an issue, I'll be happy to discuss it with you

Can't call lua functions with multiple return values
The library isn't installed on the machine for now, I believe it's only a few Makefile changes and it would be okay

Support me

You can star this repository, follow me or buy me a coffee

volpi-m / Lua-in-cpp