Example of Writing Waveform Data

The following example illustrates the steps required to allocate and set up a WAVEHDR 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; 
    } 
}