Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!uc!shamash!bls
From: bls@svl.cdc.com (brian scearce)
Newsgroups: comp.lang.c
Subject: Re: Casting pointers
Keywords: cast
Message-ID: <23590@shamash.cdc.com>
Date: 19 Jul 90 19:09:24 GMT
References: <1614@ghost.stsci.edu> <9959@crdgw1.crd.ge.com>
Sender: news@shamash.cdc.com
Lines: 35

volpe@underdog.crd.ge.com (Christopher R Volpe) writes:
>In article <1614@ghost.stsci.edu>, davids@stsci.EDU (David Silberberg) writes:
>|>If the last line above were replaced by
>|>
>|>	 ptr = (char *)ptr + num_chars;
>|>
>|>it would perform as desired.  Does casting work on an lvalue?

>I'm not sure if casting on an l-value is specified anywhere.

Harbison & Steele (section 7.5.1): "Any permissible conversion may
be invoked by a cast expression.  The result is not an lvalue."

>main()
>{ int i;
>  float f;

>  f=2.0;
>  (float) i = f;
   ^^^^^^^^^^^^^ This is not legal C.
>  printf("i==%d\n",i);
>}

>Compiled with Sun C, this program prints: i==1073741824
>Compiled with gcc, it prints: i==2

It shouldn't compile at all.  The mighty CDC C Version 2 prints,
"Operation can only be performed on lvalues", an excellent diagnostic
if I do say so myself :-)

--
Brian Scearce        \ "I tell you Wellington is a bad general, the English are
(not on CDCs behalf)  \ bad soldiers; we will settle the matter by lunch time."
bls@u02.svl.cdc.com    \   -- Napolean Bonaparte, June 18, 1815 (at Waterloo)
shamash.cdc.com!u02!bls \ From _The Experts Speak_, Cerf & Navasky