PRB: WaveOutOpen()/WaveInOpen() Returns MMSYSERR_INVALPARAM

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows, version 3.1
• The Microsoft Foundation Classes (MFC) included with:

       - Microsoft Visual C++ for Windows, version 1.52
  

SYMPTOMS

The WaveOutOpen() and WaveInOpen() functions return an MMSYSERR_INVALPARAM error when using a window handle as a callback mechanism.

CAUSE

The documentation for the WaveOutOpen() and WaveInOpen() functions specifies that the data type of the dwCallback parameter should be a DWORD. However, when the symbol STRICT is defined (using #define), HWND is no longer equated to UINT. Instead, it is a NEAR pointer. Therefore, simply casting a window handle to a DWORD fails when STRICT is defined. The following code illustrates the statement causing this error:

   WaveOutOpen(..., (DWORD) hWnd, ..., CALLBACK_WINDOW)

RESOLUTION

A simple workaround is to cast a window handle to UINT before casting it to a DWORD. For example:

   WaveOutOpen(..., (DWORD) (UINT) hWnd, ...)

MORE INFORMATION

STRICT is a macro which enhances type safety for Windows 3.1 applications. If it is defined, several data types become distinct. For instance, HDC and HWND become different types when STRICT is defined.

By default, Microsoft Foundation Classes (MFC) versions 2.0 and above use STRICT type checking. As a result, the problem described in this article usually occurs in MFC-based applications. In addition, this error occurs in any API call where a window handle is cast to a DWORD (32-bits). Please note that this article only applies to 16-bit applications.