Programming Excel with VBA and .NET

Use Flags and Constants

The uFlags argument in sndPlaySound is an example of another common C convention: you can often specify options using a long integer comprised of bit flags . I discussed those back in Chapter 3, but they haven’t been much use up till now. Bit flags are numeric constants that can be combined into a single number. The following code demonstrates using bit flags to play a sound over and over again:

Public Declare Function sndPlaySound Lib "winmm.dll" Alias _
  "sndPlaySoundA" (ByVal lpszSoundName As String, ByVal uFlags As Long) _
  As Long
Public Const SND_ASYNC = &H1        '  play asynchronously
Public Const SND_LOOP = &H8         '  loop the sound until next sndPlaySound
Public Const SND_SYNC = &H0         '  play synchronously (default)
 
Sub BeginBouncing(  )
    sndPlaySound "boing", SND_ASYNC Or SND_LOOP
End Sub
 
Sub StopBouncing(  )
    sndPlaySound "boing", SND_SYNC
End Sub

I included StopBouncing because listening to boing.wav over and over again gets really annoying. You can find constants for each function by searching for the function by name at http://msdn.microsoft.com, then you can find the corresponding values for those constants using the API Viewer or by searching WIN32API.TXT.