luaL_dostring puts nothing on the stack?

Question

I'm trying to learn the basics of interfacing Lua with C++, but I've run into a problem. I want to call a function that returns a string, and then work with the string on the C++ side, but luaL_dostring seems to put nothing on the Lua stack.

Even a simple test doesn't seem to work properly:

lua_State* lua = lua_open();
luaL_openlibs(lua);

//Test dostring.
luaL_dostring(lua, "return 'derp'");

int top = lua_gettop(lua);
cout << "stack top is " <<top << endl;

//Next, test pushstring.
lua_pushstring(lua, "derp");

top = lua_gettop(lua);
cout << "stack top is " << top << endl;

Output:

stack top is 0
stack top is 1

Any ideas?

Answer 1

Aha, found the problem. According to this page, in Lua 5.1 luaL_dostring ignores returns. The code I had would probably work in Lua 5.2.

To alter the functionality, you should use:

#undef luaL_dostring
#define luaL_dostring(L,s)  \
    (luaL_loadstring(L, s) || lua_pcall(L, 0, LUA_MULTRET, 0))