Path: utzoo!utgpu!watserv1!watmath!att!rutgers!usc!zaphod.mps.ohio-state.edu!rpi!leah!bingvaxu!vu0310
From: vu0310@bingvaxu.cc.binghamton.edu (R. Kym Horsell)
Newsgroups: comp.lang.c
Subject: Re: stupid compilers
Message-ID: <3932@bingvaxu.cc.binghamton.edu>
Date: 3 Sep 90 00:29:25 GMT
References: <163@prodix.liu.se> <24700008@sunb0.cs.uiuc.edu>
Reply-To: vu0310@bingvaxu.cc.binghamton.edu.cc.binghamton.edu (R. Kym Horsell)
Organization: SUNY Binghamton, NY
Lines: 30

In article <24700008@sunb0.cs.uiuc.edu> mccaugh@sunb0.cs.uiuc.edu writes:
\\\
>   Since un-initialized ptrs so often lead to segmentation faults, here is my
>guess as to what happened. The first declaration (char line [];) must have
>initialized variable 'line' as a char-ptr to some 0-length area, while the
>second declaration (char *line;) left 'line' un-initialized. Hence the value
>of 'line' in the first case was legitimate -- even if it addressed 0-length
\\\

Your analysis seems substantially correct -- but why guess? Try
running:

main(){
	char a[];
	char *b;
	printf("%d\n",sizeof(a));
	printf("%d\n",sizeof(b));
	}

Output:

0
4

The *complier* sure thinks ``a'' is zero length -- if any
string copy is done there you will essentially be copying
``above the stack pointer'' (if nothing else is declared local).
This *may*, but not necessarily, cause a trap (depends on the hardware).

-Kym Horsell