whichchan - Returns the active channel number
isallchan - Returns whether I/O is set to read/write all channels
short whichchan (WVFILE *wfp)
short isallchan (WVFILE *wfp)
whichchan() returns the channel number set for I/O for the waveform
associated with wfp. If the waveform is set to read/write all channels,
the channel number is -1.
isallchan returns true if the waveform is set to read/write all
channels (channel number == -1), and false otherwise.
H.T.Bunnell, Shirley Peters