Register C ++ class for use in Lua 5.2

Question

So, I read about how to create and register a C ++ class for Lua through THIS small blogging tutorial .

But just as simple, informative, and legible seems to be for an older version of Lua.

So, some of the functions / macros are either absent or have different signatures.

What does the following code look like in Lua C version 5.2?

#include <lua.h> #include <lualib.h> #include <lauxlib.h> #include <stringstream> #include <string> using namespace std; // Just a useless test class class MyClass { private: int _X; public: MyClass(int x) : _X(x) {}; ~MyClass() { Release() }; // Displays your number in a welcoming message box void Hello() { stringstream ss; ss << "Hello!" << endl << "Your number is: " << _X; string s(ss.str()); MessageBoxA(NULL, s.c_str(), "MyClass", MB_ICONINFORMATION); } void Release() { //release code goes here } }; // Functions that will create/destroy MyClass instances static int newMyClass(lua_State* L) { int n = lua_gettop(L); // Number of arguments if (n != 2) return luaL_error(L, "Got %d arguments, expected 2 (class, x)", n); // First argument is now a table that represent the class to instantiate luaL_checktype(L, 1, LUA_TTABLE); lua_newtable(L); // Create table to represent instance // Set first argument of new to metatable of instance lua_pushvalue(L, 1); lua_setmetatable(L, -2); // Do function lookups in metatable lua_pushvalue(L, 1); lua_setfield(L, 1, "__index"); // Allocate memory for a pointer to to object MyClass** s = (MyClass**)lua_newuserdata(L, sizeof(MyClass*)); int x = luaL_checknumber(L, 2); *s = new MyClass(x); luaL_getmetatable(L, "Lua.MyClass"); lua_setmetatable(L, -2); lua_setfield(L, -2, "__self"); return 1; } static int doSomethingMyClass(lua_State* L) { MyClass* c = nullptr; checkUserData(L, "Lua.MyClass", c); c->Hello(); return 0; } static int destroyMyClass(lua_State* L) { MyClass* c = nullptr; checkUserData(L, "Lua.MyClass", c); c->Release(); return 0; } // Functions that will show up in our Lua environment static const luaL_Reg gMyClassFuncs[] = { // Creation { "new", newMyClass) }, { "hello", helloMyClass }, { NULL, NULL } }; static const luaL_Reg gDestroyMyClassFuncs[] = { {"__gc", destroyMyClass}, {NULL, NULL} }; // Registers the class for use in Lua void registerMyClass(lua_State *L) { // Register metatable for user data in registry luaL_newmetatable(L, "Lua.MyClass"); luaL_register(L, 0, gDestroyMyClassFuncs); luaL_register(L, 0, gMyClassFuncs); lua_pushvalue(L, -1); lua_setfield(L, -2, "__index"); // Register the base class for instances of Sprite luaL_register(L, "MyClass", gSpriteFuncs); } 

Basically, the goal here is to write the following in Lua:

 -- Create a new MyClass instance local c = MyClass:new(5) -- Show message c:Hello() -- Should say something like "Hello! Your number is: 5" 

What do I need to change to make this work for 5.2?

Answer 1

The only function in this code that is not part of Lua 5.2 is luaL_register . Instead, use luaL_setfuncs .

You must either set the global MyClass manually or use local MyClass=require"MyClass" in your Lua code, because require no longer sets global variables.

If you embed Lua, you can simply compile it and your code with -DLUA_COMPAT_MODULE and get 5.1 functions. But think that now is the time to move the code to Lua 5.2 if you plan to use this version.