Problems with lua and classes

Post the code that has the problem - i.e. the code for Setup() as well as the code where you're passing the lua_State* into other functions. It sounds like there's a minor mistake in your code someplace, but there's no way we can find it without the code itself to look over.

Script.h
- - - - - -

extern "C"
{
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"
}

class cScript
{
public:
void Setup();
void DoFile(const char*);
void Close();

private:
lua_State* Lua;
};
- - - - -


Script.cpp
- - - - -
#include "script.h"

void cScript::Setup()
{

//Create KittyKat
/* the Lua interpreter */
lua_State* Lua;

/* initialize Lua */
Lua = lua_open();

/* load Lua base libraries */
luaL_openlibs(Lua);

return L;
}

void cScript::DoFile(const char* file)
{
luaL_dofile(Lua,file);
}

void cScript::Close()
{
lua_close(Lua);
}
- - - - - -


Main.cpp
- - - - - -
#include "engine.h" //which includes script.h


int main( int argc, char* args[] )
{
//Start of program

cScript dog;
dog.Setup();
dog.DoFile("avg.lua");
dog.Close();
getchar();

return 1;
}

Your problem is in Setup(), here:

/* the Lua interpreter */lua_State* Lua;

This is creating a local variable called Lua inside of Setup(). When you call lua_open and save the lua_State*, you are storing it into this local variable. That local variable only exists (has a scope) inside of Setup().

However, when you access the Lua variable from, say, DoFile(), you are accessing the Lua member of the cScript class. This is not the same as the Lua variable that exists only inside of Setup().

What happens, then, is that the correct lua_State* data is created and returned, then kept in the local Lua inside of Setup(). As soon as Setup() returns, that variable goes out of scope, and the correct lua_State* is now lost. Instead, you have random garbage inside the cScript::Lua member, which is what will be used next time any of cScript's member functions are called, resulting in a crash.

This is commonly known as identifier shadowing and is generally something to avoid as much as possible, because it tends to create very nasty and subtle bugs like the one you've got here.


Remove the local Lua variable in Setup() and use the Lua member consistently in all of cScript, and you should be fine.