The stack

The Lua stack can serve two purposes:

• Exchange data between C++ and Lua. Passing function arguments and retrieving function return values fit into this usage.
• Keep intermediate results. For example, we can keep a table reference in the stack until we are done with the table; we can push some values onto the stack and then pop and use them as upvalues.

The Lua stack comes in two forms:

• The public stack that comes with the Lua state. Once a Lua state is created via luaL_newstate or lua_newstate, you can pass the state around and the same Lua stack is accessible to all functions that can access the Lua state.
• The private stack for each lua_CFunction call. The stack is only accessible to a function call. Calling the same lua_CFunction multiple times will not share the same stack. So, the stack that is passed to a lua_CFunction call is private to the function call.

Pushing onto the stack

You can use lua_pushXXX functions to push a value...