Lua registered C function calling another one

Question

Say I have two C functions registered in my Lua scope:

int func1(lua_State* L)
{
    int n = lua_gettop(L);
    // Do sth here...
}

int func2(lua_State* L)
{
    int n = lua_gettop(L);
    // Do sth here...
}

The question is: can I call func2 within func1?

I found out that if several arguments are passed to func1, the value that lua_gettop() returns in func2 makes no sense.

For example, if 3 arguments are passed to func1 in my lua script, lua_gettop() returns 3 in func1, and no less than 3 in func2. This is definitely wrong since lua_gettop() should return the number of arguments passed to current function.

So should I do any stack trick before calling func2 such as setting up new stack frame or just simply should not do this?

Answer 1

lua_gettop does not return number of arguments, but rather number of items on your stack. If you mess with the stack in the calling function, it will remain messed up when you directly call another C function.

If you call it via Lua (for example using lua_cpcall), it will start with it own stack state and arguments you give it within Lua.