Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!unixhub!ditka!zinn!nuucp
From: mjv@objects.mv.com (Michael J. Vilot)
Newsgroups: comp.lang.c++
Subject: RE: istream::putback(char c)
Message-ID: <1272@zinn.MV.COM>
Date: 10 Apr 91 11:42:06 GMT
Sender: news@ditka.chicago.com (Pulitzer at ditka)
Lines: 29

>From brunix!sdm
>Newsgroups: comp.lang.c++
>Message-ID: <71302@brunix.UUCP>
>Organization: Brown University Department of Computer Science
>
>Two questions:
>
>    1.  Why am I limited to putting back the last character I 
removed?  
>        There is no such limitation for ungetc in the standard C 
library.
>
>    2.  Given that I am limited to putting back the last character I 

>        read, why does putback take a parameter?

1.  The limitation does indeed exist for C.  The ANSI C library 
definition of ungetc() includes the following caution:
  "One character putback is guaranteed.  If the ungetc function is 
called too many time on the same stream without an intervening read 
or file position on that stream, the operation may fail."

2.  For much the same reason the ANSI C function takes an argument. 
This has the virtue (? ;-) of being 'consistent' with what a C 
programmer would expect, but I agree that the semantic restrictions 
on pushing back a character tend to make the argument somewhat 
superfluous.

Mike