Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!know!sdd.hp.com!wuarchive!udel!haven!umd5!jupiter.astro.umd.edu!jjk
From: jjk@jupiter.astro.umd.edu (Jim Klavetter)
Newsgroups: comp.lang.c
Subject: SUMMARY OF  confusion with char *a and char a[NUM]
Summary: thanks, summary, and followup question
Message-ID: <7676@umd5.umd.edu>
Date: 5 Dec 90 21:23:44 GMT
References: <7656@umd5.umd.edu> <1990Dec4.214845.18949@ccu.umanitoba.ca> <28341@mimsy.umd.edu>
Sender: news@umd5.umd.edu
Reply-To: jjk@astro.umd.edu (Jim Klavetter)
Distribution: na
Organization: U of Md., Astronomy Program
Lines: 46

Thanks everyone for the end of confusion.  In addition to the typos
(NUM+1 and ":"), it was made abundantly clear to me that you can't use
a "constant" as an lvalue:
	char a[NUM];
	char *b;

	/*  malloc b for NUM things  */
	a=strchr(string, ':');	/*   ERROR  */
	b=strchr(string, ':');  /*   CORRECT   */

Of course I knew that and I shouldn't have had to post to the net.
However, the following is ok in both cases (same declarations as
above):
	strcpy(string, a);
	strcpy(string, b);
Again, it was explained to me that a is "promoted" to type char*.  Or
another way it was put was the usual "equivalence" of pointers and
arrays (and this is what the faq list details).  

I guess my followup question is more theoretical in nature:  is this a
good thing?  Why shouldn't 
	 strcpy(string, a); 
also send an error message since the man page explicitely says that a
(in this case) is char*.  Conceptutually I understand that a copy (in
this case) is fundamentally different than an equivalence (as above
with strchr()), and also that a is unambiguous in this case, but as so
many are willing to point out:  pointers are not arrays!  (and vice
versa).  Thus, the man page is asking for a pointer, but I am giving
it an array, yet it works.

I hope I am making my confusion a little clearer, here.  It is not
that I don't understand the difference between pointers and arrays,
but that the language itself, IN SOME CASES, doesn't seem to think
there is any difference.

I'm certainly not a c basher, it just seems as if this is an
inconsistency.

Thanks once again for all the help, and I hope that this doesn't
produce TOO many flames.

jjk@astro.umd.edu
Jim Klavetter (accepting mail for Athabasca and Reudi)
Astronomy
UofMD
College Park, MD  20742


Brought to you by Super Global Mega Corp .com