Wanted: a version of scanf that allows me to define getc() and ungetc()

[Robert the Good]

I have a programme that needs to read either standard input or a character
buffer, running on 4.2bsd. The way that this is currently implemented is to have
a private version of scanf, that uses my routines input() and unput() instead
of the macros getc() and ungetc().
  I am shortly moving to a VMS system, without a source license. Any ideas on
good ways to port my code?
			Robert