Windows message happen only one time.

[PacR]

#include <tchar.h>
#include <windows.h>

HDC hdc;

/*  Declare Windows procedure  */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

/*  Make the class name into a global variable  */
TCHAR szClassName[ ] = _T("CodeBlocksWindowsApp");

int WINAPI WinMain (HINSTANCE hThisInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR lpszArgument,
                     int nCmdShow)
{
    HWND hwnd; /* This is the handle for our window */
    MSG messages;            /* Here messages to the application are saved */
    WNDCLASSEX wincl;        /* Data structure for the windowclass */

    /* The Window structure */
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;      /* This function is called by windows */
    wincl.style = CS_DBLCLKS;                 /* Catch double-clicks */
    wincl.cbSize = sizeof (WNDCLASSEX);

    /* Use default icon and mouse-pointer */
    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;                 /* No menu */
    wincl.cbClsExtra = 0;                      /* No extra bytes after the window class */
    wincl.cbWndExtra = 0;                      /* structure or the window instance */
    /* Use Windows's default colour as the background of the window */
    wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

    /* Register the window class, and if it fails quit the program */
    if (!RegisterClassEx (&wincl))
        return 0;

    /* The class is registered, let's create the program*/
    hwnd = CreateWindowEx (
           0,                   /* Extended possibilites for variation */
           szClassName,         /* Classname */
           _T("My App"),       /* Title Text */
           WS_OVERLAPPEDWINDOW, /* default window */
           CW_USEDEFAULT,       /* Windows decides the position */
           CW_USEDEFAULT,       /* where the window ends up on the screen */
           200,                 /* The programs width */
           100,                 /* and height in pixels */
           HWND_DESKTOP,        /* The window is a child-window to desktop */
           NULL,                /* No menu */
           hThisInstance,       /* Program Instance handler */
           NULL                 /* No Window Creation data */
           );

    /* Make the window visible on the screen */
    hdc = GetDC(hwnd);
    ShowWindow (hwnd, nCmdShow);
    UpdateWindow(hwnd);

    /* Run the message loop. It will run until GetMessage() returns 0 */
    while (GetMessage (&messages, NULL, 0, 0))
    {
        /* Translate virtual-key messages into character messages */
        TranslateMessage(&messages);
        /* Send message to WindowProcedure */
        DispatchMessage(&messages);
    }

    /* The program return-value is 0 - The value that PostQuitMessage() gave */
    return messages.wParam;
}


/*  This function is called by the Windows function DispatchMessage()  */

LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)                  /* handle the messages */
    {
	case WM_OnlyOneTime:
            MessageBox(NULL, "This will happen only one time in this programs life.","Help", MB_OK);
	    break;

        case WM_CREATE:
            break;

        case WM_PAINT:
            break;

        case WM_DESTROY:
            ReleaseDC(hwnd, hdc);
            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
            break;
        default:                      /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}

Thank you for your help.

[kbw]

There's noting sending/posting message WM_OnlyOneTime.

[deleted account xyzzy]

WM_OnlyOneTime is not a window message as defined by MS/Windows. It isn't in <winuser.h> where the standard WM_ window messages are defined. Maybe(?) it is a custom user-defined message for the app?

What exactly are you trying to do? Explain in detail what you want to do.

When does that message get sent by Windows to your app?

[deleted account xyzzy]

16-bit Win9X is dead, unless you are creating this Win32 app for Win9X you should explicitly use Unicode for the Win32 functions and data types so your app is usable with conversion from 16-bit to 32/64 bit on modern Windows versions.

// updated for modern Windows later than Win9x/Me
// uses Unicode characters sets

#include <windows.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI wWinMain(_In_      HINSTANCE hInstance,
                    _In_opt_  HINSTANCE hPrevInstance,
                    _In_      PWSTR szCmdLine,
                    _In_      int nWinMode)
{
   static const WCHAR szAppName[] = L"WinMinApp";

   WNDCLASSEXW wc;

   wc.cbSize        = sizeof(WNDCLASSEXW);
   wc.style         = CS_HREDRAW | CS_VREDRAW;
   wc.lpfnWndProc   = WndProc;
   wc.cbClsExtra    = 0;
   wc.cbWndExtra    = 0;
   wc.hInstance     = hInstance;
   wc.hIcon         = (HICON)   LoadImageW(NULL, IDI_APPLICATION, IMAGE_ICON, 0, 0, LR_DEFAULTCOLOR);
   wc.hIconSm       = (HICON)   LoadImageW(NULL, IDI_APPLICATION, IMAGE_ICON, 0, 0, LR_DEFAULTCOLOR);
   wc.hCursor       = (HCURSOR) LoadImageW(NULL, IDC_ARROW, IMAGE_CURSOR, 0, 0, LR_SHARED);
   wc.hbrBackground = (HBRUSH) (COLOR_WINDOW + 1);
   wc.lpszMenuName  = NULL;
   wc.lpszClassName = szAppName;

   if (0 == RegisterClassExW(&wc))
   {
      MessageBoxW(NULL, L"Can't Register the Window Class!", szAppName, MB_OK | MB_ICONERROR);
      return E_FAIL;
   }

   static const WCHAR szAppTitle[] = L"Modern WinAPI Skeletal Application";

   HWND hwnd = CreateWindowW(szAppName, szAppTitle,
                             WS_OVERLAPPEDWINDOW,
                             CW_USEDEFAULT, CW_USEDEFAULT,
                             CW_USEDEFAULT, CW_USEDEFAULT,
                             NULL, NULL, hInstance, NULL);

   if (NULL == hwnd)
   {
      MessageBoxW(NULL, L"Unable to Create the Main Window!", szAppName, MB_OK | MB_ICONERROR);
      return E_FAIL;
   }

   ShowWindow(hwnd, nWinMode);
   UpdateWindow(hwnd);

   MSG msg;

   while (GetMessageW(&msg, NULL, 0, 0))
   {
      TranslateMessage(&msg);
      DispatchMessageW(&msg);
   }

   return (int) msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
   switch (message)
   {
   case WM_PAINT:
      HDC         hdc;
      PAINTSTRUCT ps;
      hdc = BeginPaint(hwnd, &ps);

      RECT rect;
      GetClientRect(hwnd, &rect);
      DrawTextW(hdc, L"Hello, Modern Windows!", -1, &rect, DT_SINGLELINE | DT_CENTER | DT_VCENTER);

      EndPaint(hwnd, &ps);
      return S_OK;

   case WM_DESTROY:
      PostQuitMessage(0);
      return S_OK;
   }

   return DefWindowProcW(hwnd, message, wParam, lParam);
}

[PacR]

George P. Thank you. Yes custom windows message is what i was looking for.

[deleted account xyzzy]

What is the custom window message supposed to represent? Why do you need to create a custom window message?

Please explain IN DETAIL what you are trying to do. This isn't the first time I've asked that.

[ETA]: I guess this topic is solved now, adios.

Elvis has left the thread, Pax!

[kigar64551]

To define a custom window message, you should do something like this:
#define WM_MyCustomMessage (WM_USER + 42)

The following are the ranges of message numbers:
0 through WM_USER –1: Messages reserved for use by the system.
WM_USER (0x400) through 0x7FFF: Integer messages for use by private window classes

This needs to be defined identically in the program that sends the message and in the program that is supposed to process (handle) the message.