Lua arguments at wrong memory location

Question

When parsing variables from lua, lua is acting strangely.

C++:

int LuaManager::SetTimer(lua_State *pLua)
{
    if (!lua_isstring(pLua, 0)) throw "expected: string";
    if (!lua_isnumber(pLua, 1)) throw "expected: number";

    std::string callback = lua_tostring(pLua, 0);
    double delay = lua_tonumber(pLua, 1);
    Timer timer = Timer(callback, delay);

    return 0;
}

lua:

SetTimer("Durp", 10);

I get a "First-chance exception at 0x76C44598: Microsoft C++ exception: char at memory location 0x00D7F588" from the line

std::string callback = lua_tostring(pLua, 0);

When I debug the code and press continue when the exception pops up it throws random variables into the variable. The same goes for the double delay.

However when I say:

std::string callback = lua_tostring(pLua, -2);
double delay = lua_tonumber(pLua, -1);

It will still give the exception but the correct variables are thrown in.

If an exception is thrown the variable is most certainly not going to contain a valid value. — Captain Obvlious, Jan 18 '15 at 19:37
Oh you're completely right such a stupid oversight of mine. Any idea though on why -1 and -2 were also returning the correct values? — R4VANG3R, Jan 18 '15 at 23:15
I wonder if compiling lua with `LUA_USE_APICHECK` would have caught this. — greatwolf, Jan 19 '15 at 05:11

score 1 · Answer 1 · answered Jan 19 '15 at 07:01

1

From my memories, the line

std::string callback = lua_tostring(pLua, 0);

should be

std::string callback = lua_tostring(pLua, 1);

because indexes in lua start at 1.

answered Jan 19 '15 at 07:01

vincentp

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Lua arguments at wrong memory location

1 Answers1