InitApp

The InitApp function creates the application message queue and installs essential application-support routines. These include a signal procedure, version-specific resource loaders, and a divide-by-zero interrupt handler.

BOOL WINAPI InitApp(HANDLE hInstance);

• hInstance — Handle to the task to be initialized. This value must be the instance handle returned in the `DI` register by the preceding `InitTask` call.

Returns nonzero in the `AX` register if successful. If the function fails, it returns zero, and the application must exit immediately.

• Because this function creates the message queue, failure to call it (or calling out of sequence) will result in an application that cannot receive messages.

/* Declaration of InitApp (often not included in windows.h) */
extern WINAPI InitApp(HANDLE hInstance);
 
int PASCAL WinMain(HANDLE hInstance, HANDLE hPrevInstance,
                   LPSTR lpCmdLine, int nCmdShow)
{
    /* InitApp is typically called in the startup code before WinMain.
       If you are writing custom startup code, call it as shown: */
    if (!InitApp(hInstance))
    {
        /* Critical error: message queue could not be created */
        return 1;
    }
 
    /* ... application code ... */
    return 0;
}

; Standard startup fragment (after InitTask and WaitEvent)
externFP        InitApp           ; declare far external
 
    push    di                    ; hInstance from InitTask (DI register)
    call    far InitApp           ; create message queue & install handlers
    or      ax, ax                ; test return value
    jz      noinit                ; jump if initialization failed
 
    ; ... proceed to call WinMain ...
 
noinit:
    mov     al, 0FFh              ; return error code
    mov     ah, 4Ch
    int     21h

• InitTask
• WaitEvent