Combobox does not add string

[indiocolifa]

the following window procedure does not add the MIDI Devices on the combo box I want, i'm using CB_ADDSTRING...

LRESULT CALLBACK wndproc (HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
{
    int         nDevices;
    MIDIOUTCAPS moutcaps[255]; 
    HWND        hwndDevices, hwndListCaps;
    
    switch (msg)
    {
    case WM_CREATE:
        
        int i;
        
        // enumerar dispositivos MIDI
        nDevices = midiOutGetNumDevs();
        
        if (nDevices == 0)
        {
            MessageBox (0, "No MIDI devices available.", "Error", MB_ICONSTOP);
            exit(EXIT_FAILURE);
        }
        
        hwndDevices = GetDlgItem(hwnd, IDC_DEVICE);
        hwndListCaps= GetDlgItem(hwnd, IDC_LISTCAPS);
        
        for (i = 0; i < nDevices; i++)
        {
            midiOutGetDevCaps(i, &moutcaps[i], sizeof(MIDIOUTCAPS));
            SendMessage(hwndDevices, CB_ADDSTRING, 0, (LPARAM)moutcaps[i].szPname); 
        }
        return 0;
        
    case WM_CLOSE:
        DestroyWindow(hwnd);
        break;
        
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
        
    }
    
    return DefWindowProc(hwnd, msg, wparam, lparam);
    
}

where is the problem?????