Window Class Registration Failed - c++

Question

I am writing the beginnings of a game as a Win32 application. Everything worked fine when I registered the class within Main.cpp, but now I'm trying to move it to a Game class to make the code easier for me to use.
Since I have moved the code into the Game class, window class registration fails. Here is my code, please note that some functions are empty simply because I haven't got that far yet.
GetLastError() returns 87.
Main.cpp
#include "Main.h"
// entry point for the program, see Game for explanation of parameters
int WINAPI WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
{
game = std::unique_ptr<Game>(new Game(hInstance, hPrevInstance, lpCmdLine, nCmdShow));
game->Init();
// main game loop
while(game->IsRunning())
{
game->HandleMessages();
game->Update(0.0f);
game->Render();
}
return EXIT_SUCCESS;
}
Game.cpp
#include "Game.h"
#include <Windows.h>
LPCWSTR g_szClassName = L"Life Simulator Window Class";
Game::Game(HINSTANCE _hInstance, // handle to an instance of the application
HINSTANCE _hPrevInstance, // handle to previous instance of the application
LPSTR _lpCmdLine, // command line parameters
int _nCmdShow) // controls how the window is show)
{
hInstance = _hInstance;
hPrevInstance = _hPrevInstance;
lpCmdLine = _lpCmdLine;
nCmdShow = _nCmdShow;
return;
}
Game::~Game(void)
{
}
bool
Game::Init()
{
// set paramaters for window class
wc.cbClsExtra = 0; // number of extra bytes to allocate after window class, not needed but showing for verbosity
wc.cbSize = sizeof(WNDCLASSEX); // stores the size of the WNDCLASSEX structure, helping future proof your application in case new fields are added
wc.cbWndExtra = 0; // similar to cbClsExtra, but refers to the window itself rather than the window class
wc.hbrBackground = (HBRUSH) (COLOR_WINDOW); // handle to a background brush, in this case it's simply a colour cast into a brush handle
wc.hCursor = LoadCursor(NULL, IDC_ARROW); // handle to cursor, first paramater is a handle to the instance of the application containing the cursor (not needed in this case), second is the resource identifier
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION); // similar to hCursor, but for the application icon instead
wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION); // as above, but for the smaller version of the icon
wc.hInstance = hInstance; // handle to the instance of the application that contains the window procedure
wc.lpfnWndProc = Game::WndProc; // a pointer to the window procedure
wc.lpszClassName = g_szClassName; // the window class name (see global variables)
wc.lpszMenuName = NULL; // specifies the resource name of the menu, which isn't used in this case
wc.style = CS_HREDRAW | CS_VREDRAW; // style for the window class, which in this case means to redraw if it's affected (i.e. resized or moved) vertically or horizontally
// register the window class
if(!RegisterClassEx(&wc))
{
// this code is executed if the window class fails to register successfully
MessageBox(NULL, // an owner for the message box can be specified here
L"Window Class Registation Failed.", // message to be displayed
L"Fatal Error", // title of the message box
MB_ICONEXCLAMATION | MB_OK); // type of message box, in this case it has an exclamation icon and an OK button
return EXIT_FAILURE; // return EXIT_FAILURE to indicate that the program closed due to a runtime error
}
// create the window
hWnd = CreateWindowEx(WS_EX_OVERLAPPEDWINDOW, // extended window style
g_szClassName, // class of window to be created (this is the window class created earlier)
L"Life Simulator", // title of the window
WS_OVERLAPPEDWINDOW, // window style
CW_USEDEFAULT, // x position of the window, here default values are used
CW_USEDEFAULT, // as above, but for the y position
wndWidth, // width of the window
wndHeight, // height of the window
NULL, // parent window, if it has one
NULL, // handle to the menu for the window
hInstance, // handle to the instance of the application
NULL); // lpParam can be passed on here
if(hWnd == NULL)
{
// this code is executed if the creating the window failed
MessageBox(NULL, // an owner for the message box can be specified here
L"Window Creation Failed.", // message to be displayed
L"Fatal Error", // title of the message box
MB_ICONEXCLAMATION | MB_OK); // type of message box, in this case it has an exclamation icon and an OK button
return EXIT_FAILURE; // return EXIT_FAILURE to indicate that the program closed due to a runtime error
}
ShowWindow(hWnd, // handle to the window to be shown
nCmdShow); // passed on from WinMain, controls how the window should be shown (i.e. minimised or maximised)
UpdateWindow(hWnd); // forces the window the be updated by forcing a WM_PAINT message past the application queue
}
// window procedure for the game
LRESULT CALLBACK
Game::WndProc(HWND hWnd, // handle to the window
UINT msg, // message to be processed
WPARAM wParam, // additional message information
LPARAM lParam) // even more additional message information
{
switch(msg)
{
case WM_CLOSE: // red X has been clicked
DestroyWindow(hWnd); // sends WM_DESTROY to the window
break;
case WM_DESTROY: // some part of the program has requested the window to be destroyed
PostQuitMessage(0); // sends quit message to window
break;
default: // unhandled messages
return DefWindowProc(hWnd, msg, wParam, lParam);// windows will handle any messages that haven't been handled explicitly
}
return 0;
}
void
Game::HandleMessages()
{
while(PeekMessage(&msg, // container for the message
NULL, // when multiple windows are used, you can specify which one here
0, // used to filter messages, not needed here
0, // as above
PM_REMOVE)) // remove messages after they've been processed
{
TranslateMessage(&msg); // turns virtual key messages into character messages
DispatchMessage(&msg); // sends the message on to its window procedure (i.e. WndProc)
}
return;
}
void
Game::Update(float elapsedTime)
{
return;
}
void
Game::Render()
{
return;
}
Previously working Main.cpp
#include <Windows.h>
// global variables
LPCWSTR g_szClassName = L"Life Simulator Window Class"; // the L casts the string to a wide string and it is called g_szClassName by convention, making the code easier to read for others
static const int wndHeight = 800;
static const int wndWidth = 600;
// window procedure for the program
LRESULT CALLBACK WndProc(HWND hWnd, // handle to the window
UINT msg, // message to be processed
WPARAM wParam, // additional message information
LPARAM lParam) // even more additional message information
{
switch(msg)
{
case WM_CLOSE: // red X has been clicked
DestroyWindow(hWnd); // sends WM_DESTROY to the window
break;
case WM_DESTROY: // some part of the program has requested the window to be destroyed
PostQuitMessage(0); // sends quit message to window
break;
default: // unhandled messages
return DefWindowProc(hWnd, msg, wParam, lParam);// windows will handle any messages that haven't been handled explicitly
}
}
// entry point for the program
int WINAPI WinMain(HINSTANCE hInstance, // handle to an instance of the application
HINSTANCE hPrevInstance, // handle to previous instance of the application
LPSTR lpCmdLine, // command line parameters
int nCmdShow) // controls how the window is show
{
// initialise variables
HWND hWnd; // handle to window
WNDCLASSEX wc; // window class container
MSG msg; // window message container
// set paramaters for window class
wc.cbClsExtra = 0; // number of extra bytes to allocate after window class, not needed but showing for verbosity
wc.cbSize = sizeof(WNDCLASSEX); // stores the size of the WNDCLASSEX structure, helping future proof your application in case new fields are added
wc.cbWndExtra = 0; // similar to cbClsExtra, but refers to the window itself rather than the window class
wc.hbrBackground = (HBRUSH) (COLOR_WINDOW); // handle to a background brush, in this case it's simply a colour cast into a brush handle
wc.hCursor = LoadCursor(NULL, IDC_ARROW); // handle to cursor, first paramater is a handle to the instance of the application containing the cursor (not needed in this case), second is the resource identifier
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION); // similar to hCursor, but for the application icon instead
wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION); // as above, but for the smaller version of the icon
wc.hInstance = hInstance; // handle to the instance of the application that contains the window procedure
wc.lpfnWndProc = WndProc; // a pointer to the window procedure
wc.lpszClassName = g_szClassName; // the window class name (see global variables)
wc.lpszMenuName = NULL; // specifies the resource name of the menu, which isn't used in this case
wc.style = CS_HREDRAW | CS_VREDRAW; // style for the window class, which in this case means to redraw if it's affected (i.e. resized or moved) vertically or horizontally
// register the window class
if(!RegisterClassEx(&wc))
{
// this code is executed if the window class fails to register successfully
MessageBox(NULL, // an owner for the message box can be specified here
L"Window Class Registation Failed.", // message to be displayed
L"Fatal Error", // title of the message box
MB_ICONEXCLAMATION | MB_OK); // type of message box, in this case it has an exclamation icon and an OK button
return EXIT_FAILURE; // return EXIT_FAILURE to indicate that the program closed due to a runtime error
}
// create the window
hWnd = CreateWindowEx(WS_EX_OVERLAPPEDWINDOW, // extended window style
g_szClassName, // class of window to be created (this is the window class created earlier)
L"Life Simulator", // title of the window
WS_OVERLAPPEDWINDOW, // window style
CW_USEDEFAULT, // x position of the window, here default values are used
CW_USEDEFAULT, // as above, but for the y position
wndWidth, // width of the window
wndHeight, // height of the window
NULL, // parent window, if it has one
NULL, // handle to the menu for the window
hInstance, // handle to the instance of the application
NULL); // lpParam can be passed on here
if(hWnd == NULL)
{
// this code is executed if the creating the window failed
MessageBox(NULL, // an owner for the message box can be specified here
L"Window Creation Failed.", // message to be displayed
L"Fatal Error", // title of the message box
MB_ICONEXCLAMATION | MB_OK); // type of message box, in this case it has an exclamation icon and an OK button
return EXIT_FAILURE; // return EXIT_FAILURE to indicate that the program closed due to a runtime error
}
ShowWindow(hWnd, // handle to the window to be shown
nCmdShow); // passed on from WinMain, controls how the window should be shown (i.e. minimised or maximised)
UpdateWindow(hWnd); // forces the window the be updated by forcing a WM_PAINT message past the application queue
// message loop
while(true){ // program closes instantly otherwise
while(PeekMessage(&msg, // container for the message
NULL, // when multiple windows are used, you can specify which one here
0, // used to filter messages, not needed here
0, // as above
PM_REMOVE)) // remove messages after they've been processed
{
TranslateMessage(&msg); // turns virtual key messages into character messages
DispatchMessage(&msg); // sends the message on the its window procedure (i.e. WndProc)
}
}
return msg.wParam; // contains the exit code from the last message, most likely WM_QUIT
}
Game.h
#pragma once
#include <Windows.h>
class Game
{
public:
Game(HINSTANCE hInstance, // handle to an instance of the application
HINSTANCE hPrevInstance, // handle to previous instance of the application
LPSTR lpCmdLine, // command line parameters
int nCmdShow); // controls how the window is show
~Game(void);
bool Init();
bool IsRunning(){return isRunning;}
// window procedure for the game
static LRESULT CALLBACK WndProc(HWND hWnd, // handle to the window
UINT msg, // message to be processed
WPARAM wParam, // additional message information
LPARAM lParam); // even more additional message information
void HandleMessages(); // messages are translated and dispatched here
void Update(float elapsedTime); // game logic
void Render(); // display results
public: // changed to public until I can get it all working
bool isRunning;
HINSTANCE hInstance;
HINSTANCE hPrevInstance;
LPSTR lpCmdLine;
int nCmdShow;
LPCWSTR g_szClassName; // the L casts the string to a wide string and it is called g_szClassName by convention, making the code easier to read for others
static const int wndHeight = 600; // window height
static const int wndWidth = 800; // window width
HWND hWnd; // handle to window
WNDCLASSEX wc; // window class container
MSG msg; // window message container
};

Answer 1

The problem is that you have g_szClassName declared as both a member variable and a global variable. The member variable g_szClassName is not initialized anywhere and can point to anything.
There is also no reason to have wc and msg declared as member variables as they do not need to persist throughout the lifetime of the object. Make them local variables instead.