Lua toString exception for boolean value - c++

Question

I wrote a simple lua function which uses 'C++' function to execute. As my intention of creating a 'C++' function is to use the same across all lua functions to update the 'C++' variables. It works fine for numbers, but when I tried it for boolean values, it give me exception when convert to string.
Here is my code snippet.
C++ code.
#include <lua.hpp>
/* the Lua interpreter */
lua_State *luaState;
std::map<lua_State *, CLuaTest *> luaFbtlookup;
void CLuaTest::CLuaTest() {
// initialize Lua
luaState = luaL_newstate();
lua_register(luaState, "get_value", get_value); // func to get values
lua_register(luaState, "set_value", set_value); // func to set values
// load Lua base libraries
luaL_openlibs(luaState);
luaL_dofile(luaState, "C:\LuaTest.lua");
luaFbtlookup.insert(make_pair(luaState, this));
}
int get_value(lua_State *L);
int set_value(lua_State *L);
extern "C++" int get_value(lua_State *L)
{
string lightName = lua_tostring(L, 1);
FbTLuaLookup::iterator iter = luaFbtlookup.find(L);
if (iter != luaFbtlookup.end()) {
lua_pushstring(L, iter->second->getValueFrom(lightName).c_str());
return 1; // do not return zero
}
return 1;
}
extern "C++" int set_value(lua_State *L)
{
string lightName = lua_tostring(L, 1);
if (NULL == lua_tostring(L, 2))
{
printf("WARNING : Invalid String Argument / Cannot convert arg#2 to string");
}
else {
string value = lua_tostring(L, 2);
FbTLuaLookup::iterator iter = luaFbtlookup.find(L);
if (iter != luaFbtlookup.end()) {
iter->second->setValueTo(lightName, value);
lua_pushnumber(L, true);
return 1; // do not return zero
}
}
return 1;
}
CLuaTest::ExecuteScript(enum Seq) {
switch(Seq) {
case 0:
lua_getglobal(luaState, "AllLightsOff");
break;
case 1:
lua_getglobal(luaState, "RedLightOn");
break;
case 2:
lua_getglobal(luaState, "AmberLightOn");
break;
case 3:
lua_getglobal(luaState, "GreenLightOn");
break;
}
}
My lua script:
function AllLightsOff
set_value("RedLight", 0)
set_value("AmberLight",0)
set_value("GrenLight",0)
end
function RedLightOn
set_value("RedLight", 1)
set_value("AmberLight",0)
set_value("GrenLight",0)
end
function AmberLightOn
set_value("RedLight", 0)
set_value("AmberLight",1)
set_value("GrenLight",0)
end
function GreenLightOn
set_value("RedLight", 0)
set_value("AmberLight",0)
set_value("GrenLight",1)
end
Things work fine with the above code, but when I tried to change the set value to use boolean values like set_value("RedLight", False) I get warning message printing. Should I need to pass False as string?

Answer 1

Lua doesn't have False, so it simply tries to read global _G["False"] which is of course nil.
It has false keyword, however, but it wouldn't work either: lua_tostring is working only for numbers and strings.
We don't see setValueTo code, so it is hard to guess how it works.
If you simply want to pass bool value to it, use lua_toboolean, but be aware that it treats 0 as true (as Lua in general).
If you want to pass "True" or "False" as strings, then yes, you must write set_value("RedLight", "False")
As a side note, consider reading how to implement lua_CFunction protocol. Now, if get_value can't find lightName, it will return the last passed parameter as its result.