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====== InitApp ======

===== Brief =====

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.

===== Syntax =====

<code c>
BOOL WINAPI InitApp(HANDLE hInstance);
</code>

===== Parameters =====

  * **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.

===== Return Code =====

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

===== Notes =====

  * 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.

===== Example Code =====

==== C Binding ====
<code c>
/* 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;
}
</code>

==== MASM Binding ====
<code asm>
; 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
</code>

===== See also =====

  * [[en:docs:win16:api:kernel:inittask|InitTask]]
  * [[en:docs:win16:api:kernel:waitevent|WaitEvent]]

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