test.cpp

//  g++ -std=c++11 test.cpp `pkg-config --cflags lua51`  `pkg-config --libs lua51`  -o ver-lua    && ./ver-lua
//  g++ -std=c++11 test.cpp `pkg-config --cflags luajit` `pkg-config --libs luajit` -o ver-luajit && ./ver-luajit

#include    <iostream>
#include    <sstream>
#include    <string>

#include    <lua.hpp>

#define     PRINT_LUA_VERSION \
"if not jit then" \
"   print(_VERSION) " \
"else" \
"   print(jit.version) " \
"end"

inline float mystof(const std::string &str) {
    return atof(str.c_str());
}
#define stof mystof

inline std::string ftos(float f) {
    std::ostringstream oss;
    oss << f;
    return oss.str();
}

int my_func(lua_State* L)
{
    float x = (float)lua_tonumber(L, 1);
    std::string str = ftos(x);
    std::cout << "1st param(string):" << str << std::endl;

    lua_settop(L, 0);
    //lua_pushnumber(L, stod(str));     // double
    lua_pushnumber(L, stof(str));       // float
    return 1;
}

int main() {
    lua_State* L = luaL_newstate();
    luaL_openlibs(L);
    lua_register(L, "my_func", my_func);

    if (luaL_dostring(L, PRINT_LUA_VERSION)) {
        lua_close(L);
        exit(EXIT_FAILURE);
    }

    if (luaL_dostring(L, "print('function result  :' .. my_func(0.1))")) {
        lua_close(L);
        exit(EXIT_FAILURE);
    }
    lua_close(L);
    return 0;
}