GetWindowThreadProcessId function (winuser.h)

Retrieves the identifier of the thread that created the specified window and, optionally, the identifier of the process that created the window.

DWORD GetWindowThreadProcessId(
  [in]            HWND    hWnd,
  [out, optional] LPDWORD lpdwProcessId
);

[in] hWnd

Type: HWND

A handle to the window.

[out, optional] lpdwProcessId

Type: LPDWORD

A pointer to a variable that receives the process identifier. If this parameter is not NULL, GetWindowThreadProcessId copies the identifier of the process to the variable; otherwise, it does not. If the function fails, the value of the variable is unchanged.

Type: DWORD

If the function succeeds, the return value is the identifier of the thread that created the window. If the window handle is invalid, the return value is zero. To get extended error information, call GetLastError.

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