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====== PostQuitMessage ======

===== Brief =====

The **PostQuitMessage** function posts a message to Windows indicating that an application is requesting to terminate execution (quit). This function is typically used in response to a `WM_DESTROY` message.

===== Syntax =====

<code c>
VOID WINAPI PostQuitMessage(int nExitCode);
</code>

===== Parameters =====

  * **nExitCode** — Specifies an application-defined exit code. It must be the **wParam** parameter of the `WM_QUIT` message.

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

This function does not return a value.

===== Notes =====

  * The PostQuitMessage function posts a `WM_QUIT` message to the application and returns immediately; the function simply indicates to the system that the application will request to quit some time in the future.
  * When the application receives the `WM_QUIT` message, it should exit the message loop in the main function and return control to Windows.

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

==== C Binding ====
<code c>
#include <windows.h>

LRESULT CALLBACK __export WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
    }
    return DefWindowProc(hwnd, msg, wParam, lParam);
}

int WINAPI WinMain(HANDLE hInstance, HANDLE hPrevInstance,
                   LPSTR lpCmdLine, int nCmdShow)
{
    MSG msg;

    /* ... window class registration and creation ... */

    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}
</code>

==== MASM Binding ====
<code asm>
EXTRN PostQuitMessage:FAR

WndProc PROC FAR
    cmp     ax, WM_DESTROY
    je      handle_destroy
    ; ... other messages ...

handle_destroy:
    push    0                    ; nExitCode = 0
    call    PostQuitMessage
    xor     ax, ax               ; return 0 (message handled)
    retf
WndProc ENDP

; Message loop that catches WM_QUIT
WinMain PROC FAR
    ; ... initialization ...

message_loop:
    lea     ax, msg
    push    ax                   ; lpMsg
    push    0                    ; hWnd
    push    0                    ; wMsgFilterMin
    push    0                    ; wMsgFilterMax
    call    GetMessage
    cmp     ax, 0
    je      exit_app             ; FALSE — WM_QUIT received

    lea     ax, msg
    push    ax
    call    TranslateMessage
    lea     ax, msg
    push    ax
    call    DispatchMessage
    jmp     message_loop

exit_app:
    mov     ax, msg.wParam       ; return exit code from WM_QUIT
    retf
WinMain ENDP
</code>

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

  * [[en:docs:win16:api:user:messagebox|MessageBox]]
  * [[en:docs:win16:api:user:initapp|InitApp]]
  * [[en:docs:win16:api:user:getmessage|GetMessage]]

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