win32 program for multiple windows - c++

Question

i am trying to write a program for multiple windows. In this program when user left click on one window it should a message which window was clicked. Here is my code:
#include<Windows.h>
// Store handles to the main window and application instance globally.
HWND ghFirstWnd =0;
HWND ghSecondWnd=0;
HWND ghThirdWnd=0;
HINSTANCE ghAppInst=0;
//========================================================================================
// WINDOW 1
// Step 1: Define and implement the window procedure.
LRESULT CALLBACK
WndProc1(HWND hWnd,UINT msg,WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
// Handle left mouse button click message.
case WM_LBUTTONDOWN:
MessageBox(0,L"first window ",L"MSG",MB_OK);
return 0;
// Handle key down message.
case WM_KEYDOWN:
if(wParam==VK_ESCAPE)
if(MessageBox(hWnd,L"sure ??",L"confirmation",MB_YESNO)==IDYES)
DestroyWindow(ghFirstWnd);
return 0;
// Handle destroy window message.
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hWnd,msg,wParam,lParam);
}
//========================================================================================
// WINDOW 2
//========================================================================================
LRESULT CALLBACK
WndProc2(HWND hWnd,UINT msg, WPARAM wParam,LPARAM lParam)
{
switch(msg)
{
case WM_LBUTTONDOWN:
MessageBox(0,L"second window",L"msg",MB_OK);
return 0;
}
return DefWindowProc(hWnd,msg,wParam,lParam);
}
//========================================================================================
// WINDOW 3
//========================================================================================
LRESULT CALLBACK
WndProc3(HWND hWnd,UINT msg,WPARAM wParam,LPARAM lParam)
{
switch(msg)
{
case WM_LBUTTONDOWN:
MessageBox(0,L"third window",L"msg",MB_OK);
return 0;
}
return DefWindowProc(hWnd,msg,wParam,lParam);
}
// WinMain: Entry point for windows application.
int WINAPI
WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR cmdLine,int showCmd)
{
// Save handle to application instance.
ghAppInst=hInstance;
// Step 2: Fill out a WNDCLASS instance.
WNDCLASS wc1;
wc1.style =CS_HREDRAW|CS_VREDRAW;
wc1.lpfnWndProc =WndProc1;
wc1.cbClsExtra=0;
wc1.cbWndExtra=0;
wc1.hInstance=ghAppInst;
wc1.hIcon=::LoadIcon(0,IDI_APPLICATION);
wc1.hCursor=::LoadCursor(0,IDC_ARROW);
wc1.hbrBackground=(HBRUSH)::GetStockObject(WHITE_BRUSH);
wc1.lpszMenuName=0;
wc1.lpszClassName=L"first class";
// Window 2
WNDCLASS wc2;
wc2.style=CS_HREDRAW|CS_VREDRAW;
wc2.lpfnWndProc=WndProc2;
wc2.cbClsExtra=0;
wc2.cbWndExtra=0;
wc2.hInstance=ghAppInst;
wc2.hIcon=::LoadIcon(0,IDI_APPLICATION);
wc2.hCursor=::LoadCursor(0,IDC_ARROW);
wc2.hbrBackground=(HBRUSH)::GetStockObject(WHITE_BRUSH);
wc2.lpszMenuName=0;
wc2.lpszClassName=L"second class";
// Window 3
WNDCLASS wc3;
wc3.style=CS_HREDRAW|CS_VREDRAW;
wc3.lpfnWndProc=WndProc3;
wc3.cbClsExtra=0;
wc3.cbWndExtra=0;
wc3.hInstance=ghAppInst;
wc3.hIcon=::LoadIcon(0,IDI_APPLICATION);
wc3.hCursor=::LoadCursor(0,IDC_ARROW);
wc3.hbrBackground=(HBRUSH)::GetStockObject(WHITE_BRUSH);
wc3.lpszMenuName=0;
wc3.lpszClassName=L"third class";
// Step 3: Register with WNDCLASS instance with windows.
RegisterClass(&wc1);
RegisterClass(&wc2);
RegisterClass(&wc3);
// Step 4: Create the window, and save the handle in global window handle variable ghMainWnd.
ghFirstWnd=::CreateWindow(L"MyWndClassName",L"MyWindow1",WS_OVERLAPPEDWINDOW,0,0,50,50,0,0,ghAppInst,0);
ghSecondWnd=::CreateWindow(L"MyWndClassName",L"MyWindow2",WS_OVERLAPPEDWINDOW,50,0,50,50,0,0,ghAppInst,0);
ghThirdWnd=::CreateWindow(L"MyWndClassName",L"MyWindow3",WS_OVERLAPPEDWINDOW,100,0,50,50,0,0,ghAppInst,0);
if(ghFirstWnd==0)
{
::MessageBox(0,L"create window1-failed",0,0);
return false;
}
if(ghSecondWnd==0)
{
::MessageBox(0,L"create window2 failed",0,0);
return false;
}
if(ghThirdWnd==0)
{
::MessageBox(0,L"create window3 failed",0,0);
return false;
}
// Step 5: Show and update the window.
ShowWindow(ghFirstWnd,showCmd);
UpdateWindow(ghFirstWnd);
ShowWindow(ghSecondWnd,showCmd);
UpdateWindow(ghSecondWnd);
ShowWindow(ghThirdWnd,showCmd);
UpdateWindow(ghThirdWnd);
// Step 6: Enter the message loop and don't quit until a WM_QUIT message is received.
MSG msg;
ZeroMemory(&msg,sizeof(MSG));
while(GetMessage(&msg,0,0,0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
// Return exit code back to operating system.
return(int)msg.wParam;
}
problem is when i try to execute the code it just say create window1- failed!!

Answer 1

Cutting the program down, you can end up with something similar to this (I've made a couple changes to the code itself, but it should still work in C++03):
#include <Windows.h>
int WINAPI
WinMain(HINSTANCE hInstance, HINSTANCE, PSTR,int showCmd)
{
WNDCLASS wc1 = {};
wc1.style = CS_HREDRAW|CS_VREDRAW;
wc1.lpfnWndProc = DefWindowProc;
wc1.hInstance = hInstance;
wc1.hIcon = ::LoadIcon(0,IDI_APPLICATION);
wc1.hCursor = ::LoadCursor(0,IDC_ARROW);
wc1.hbrBackground = (HBRUSH)::GetStockObject(WHITE_BRUSH);
wc1.lpszClassName = L"first class";
RegisterClass(&wc1);
HWND ghFirstWnd = ::CreateWindow(L"MyWndClassName",L"MyWindow1",WS_OVERLAPPEDWINDOW,0,0,50,50,0,0,hInstance,0);
if(!ghFirstWnd)
{
::MessageBox(0,L"create window1-failed",0,0);
return 1;
}
return 0;
}
With this little code, it's much easier to spot your mistake. Your window class is named "first class", but in your CreateWindow call, you use a class named "MyWndClassName". The class cannot be found, so no window can be created using it.
On a side note, you have little error checking. One thing that would really beef it up is using GetLastError appropriately.

Answer 2

CreateWindow function returns handle to the windows or when fails then returns NULL.
So replace 'if(ghFirstWnd==0)" with "if(ghFirstWnd==NULL)" and check what happens. I'm not sure because I don't use Win32.
If only "create window1-failed" message is displaying maybe try to replace "if(ghSecondWnd==0)" with "if(ghSecondWnd==1)" and then two message boxes should appear.