Operating on global variables
Lua global variables are accessible for the whole Lua state. Consider this Lua code:
whom = "C++"
function hello()
print("Hello " .. whom)
end
The hello function uses the global variable whom to print out a greeting.
How do we get and set this Lua global variable from C++? We will now extend LuaExecutor to do this and use the hello function to test it. In this chapter, we will only implement the method to work with string variables to focus primarily on the mechanism.
Getting global variables
You use the Lua library lua_getglobal function to get global variables. Its prototype is as follows:
int lua_getglobal (lua_State *L, const char *name);
lua_getglobal expects two parameters. The first one is the Lua state. The second one is the name for the global variable. lua_getglobal pushes the value of the global variable onto the stack and returns its type. The types are defined as follows:
