Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!ames!ncar!boulder!sunybcs!rutgers!bellcore!texbell!uhnix1!sugar!ficc!walker
From: walker@ficc.uu.net (Walker Mangum)
Newsgroups: comp.lang.c
Subject: Re: Why are character arrays special (equal rights for structs)
Summary: try this if you thing char *msg and char msg[] are the same!
Message-ID: <3033@ficc.uu.net>
Date: 7 Feb 89 22:37:40 GMT
References: <19742@uflorida.cis.ufl.EDU> <15833@mimsy.UUCP>
Organization: Adytum, Inc.
Lines: 58

In article <15833@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes:
> In article <19742@uflorida.cis.ufl.EDU> thoth@beach.cis.ufl.edu
> From: chris@umcp-cs.UUCP (Chris Torek)
> 
> In article <138@darth.UUCP> gary@darth.UUCP (Gary Wisniewski) writes:
> >As far as your question about "char *help[]" and "char **help": the two
> >forms are IDENTICAL to virtually every C compiler (that's worth its
> >salt).  Arrays in C are merely special cases of pointers.  In other
> >words, both forms are correct.
> 

[ K&R quotes deleted ]

> 	char	msg0[] = "Hello, world";
> 	char	*msg1 = "Hello, world";
> 
> Given both declarations,
> 
> 	printf("%s\n", msg0);
> 
> and
> 
> 	printf("%s\n", msg1);
> 
> produce the same output.  Yet msg0 and msg1 are not the same:
> 
> 	printf("%d %d\n", sizeof (msg0), sizeof (msg1));
> 

An important difference is, for any C compiler "that's worth its salt",
msg0 may not *not* be used as an lvalue!

Try this on your compiler:

char	msg0[] = "Hello, world";
char	*msg1 = "Hello, world";

main(argc,argv)
int argc;
char *argv[];

{
    msg1 = msg0;   /* this is ok - msg1 is a pointer, a legal "lvalue"		 */
    msg0 = msg1;   /* this better fail if your compiler is "worth its salt"! */
                   /* msg0 is the address of an array, and may not be        */
                   /* reassigned.  In K&R terms, it may be used only as an   */
				   /* "rvalue", not an "lvalue"								 */
}

I get the following:
x.c(10) : error 106: `=' : left operand must be lvalue


-- 
Walker Mangum                                  |  Adytum, Incorporated
phone: (713) 333-1509                          |  1100 NASA Road One  
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