Example of Writing Waveform Data

The following example illustrates the steps required to allocate and set up a WAVEHDR3CAL0JU structure and write a block of data to a waveform output device.

// Global variables.

HANDLE hData  = NULL;  // handle of waveform data memory

HPSTR  lpData = NULL;  // pointer to waveform data memory

void WriteWaveData(void)

{ 

    HWAVEOUT    hWaveOut;

    HGLOBAL     hWaveHdr;

    LPWAVEHDR   lpWaveHdr;

    HMMIO       hmmio;

    UINT        wResult;

    HANDLE      hFormat;

    WAVEFORMAT  *pFormat;

    DWORD       dwDataSize;

    // Open a waveform device for output using window callback.

    if (waveOutOpen((LPHWAVEOUT)&hWaveOut, WAVE_MAPPER,

                    (LPWAVEFORMAT)pFormat,

                    (LONG)hwndApp, 0L, CALLBACK_WINDOW))

    { 

        MessageBox(hwndApp,

                   "Failed to open waveform output device.",

                   NULL, MB_OK | MB_ICONEXCLAMATION);

        LocalUnlock(hFormat);

        LocalFree(hFormat);

        mmioClose(hmmio, 0);

        return;

    }

    // Allocate and lock memory for the waveform data.

    hData = GlobalAlloc(GMEM_MOVEABLE | GMEM_SHARE, dwDataSize );

    if (!hData)

    { 

        MessageBox(hwndApp, "Out of memory.",

                   NULL, MB_OK | MB_ICONEXCLAMATION);

        mmioClose(hmmio, 0);

        return;

    }

    if ((lpData = GlobalLock(hData)) == NULL)

    { 

        MessageBox(hwndApp, "Failed to lock memory for data chunk.",

                   NULL, MB_OK | MB_ICONEXCLAMATION);

        GlobalFree(hData);

        mmioClose(hmmio, 0);

        return;

    }

    // Read the waveform data subchunk.

    if(mmioRead(hmmio, (HPSTR) lpData, dwDataSize) != (LRESULT)dwDataSize)

    { 

        MessageBox(hwndApp, "Failed to read data chunk.",

                   NULL, MB_OK | MB_ICONEXCLAMATION);

        GlobalUnlock(hData);

        GlobalFree(hData);

        mmioClose(hmmio, 0);

        return;

    }

    // Allocate and lock memory for the header.

    hWaveHdr = GlobalAlloc(GMEM_MOVEABLE | GMEM_SHARE,

        (DWORD) sizeof(WAVEHDR));

    if (hWaveHdr == NULL)

    { 

        GlobalUnlock(hData);

        GlobalFree(hData);

        MessageBox(hwndApp, "Not enough memory for header.",

            NULL, MB_OK | MB_ICONEXCLAMATION);

        return;

    }

    lpWaveHdr = (LPWAVEHDR) GlobalLock(hWaveHdr);

    if (lpWaveHdr == NULL)

    { 

        GlobalUnlock(hData);

        GlobalFree(hData);

        MessageBox(hwndApp,

            "Failed to lock memory for header.",

            NULL, MB_OK | MB_ICONEXCLAMATION);

        return;

    }

    // After allocation, set up and prepare header.

    lpWaveHdr->lpData = lpData;

    lpWaveHdr->dwBufferLength = dwDataSize;

    lpWaveHdr->dwFlags = 0L;

    lpWaveHdr->dwLoops = 0L;

    waveOutPrepareHeader(hWaveOut, lpWaveHdr, sizeof(WAVEHDR));

    // Now the data block can be sent to the output device. The

    // waveOutWrite function returns immediately and waveform

    // data is sent to the output device in the background.

    wResult = waveOutWrite(hWaveOut, lpWaveHdr, sizeof(WAVEHDR));

    if (wResult != 0)

    { 

        waveOutUnprepareHeader(hWaveOut, lpWaveHdr,

                               sizeof(WAVEHDR));

        GlobalUnlock( hData);

        GlobalFree(hData);

        MessageBox(hwndApp, "Failed to write block to device",

                   NULL, MB_OK | MB_ICONEXCLAMATION);

        return;

    }

}