LNK2019: Calling a function in WinMain [duplicate] - c++

Question

This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 9 years ago.
I've searched everywhere and can't seem to find the answer. Nobody has made anything like this apparently. I'm trying to get input from a user.
while(!done)
{
PeekMessage(&msg,NULL,NULL,NULL,PM_REMOVE);
if (msg.message == WM_QUIT) {
done = true; //if found, quit app
} else if (msg.message == WM_KEYDOWN) {
game->KeyDown(msg.wParam);
} else if (msg.message == WM_KEYUP) {
game->KeyUp(msg.wParam);
} else {
/* Translate and dispatch to event queue*/
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
return msg.wParam;
When I run it it gives me the error:
error LNK2019: unresolved external symbol "public: void __thiscall Game::KeyDown(unsigned int &)" (?KeyDown#Game##QAEXAAI#Z) referenced in function _WinMain#16
I have everything defined in the header of the game class... It's subsystem is set to nothing, but the "(/SUBSYSTEM:WINDOWS)" works..

Answer 1

Piece of cake. "unresolved external symbol" most commonly means you declared a function without specifying what it does. Consider the following example:
void undefined();
void LNK2019()
{
undefined(); //the offending line
}
void main()
{
//doesn't even have to do anything; it's not a runtime error
}
The function LNK2019() calls undefined(), but you never told undefined() what to do. Your linker doesn't know what to make of the line. In your specific case, I'm betting Game::KeyDown doesn't have a body.
A few other comments on your code:
For Windows messages, avoid if-else trees; use switch-case. It's commonly faster, and definitely more readable.
I've never seen messages handled in a loop like that. Your Windows Procedure (whose function is commonly shortened to WndProc) should handle all Windows messages - the entire purpose of DispatchMessage is to send messages to that function.