Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!decwrl!adobe!hawley
From: hawley@adobe.COM (Steve Hawley)
Newsgroups: comp.sys.mac.programmer
Subject: Re: THINK C 4.0 bug?
Message-ID: <6280@adobe.UUCP>
Date: 5 Sep 90 17:06:23 GMT
References: <5364@munnari.oz.au>
Reply-To: hawley@adobe.UUCP (Steve Hawley)
Organization: Adobe Systems Incorporated, Mountain View
Lines: 59

In article <5364@munnari.oz.au> iand@mullian.ee.mu.OZ.AU (Ian Robert DOBSON) writes:
>I just went out and bought THINK C 4.0 and have come across an interesting
>bug.  Using the "ANSI" and "MacTraps" libraries with default project settings
>(384K, no 68020/68881 etc.) bombed the machine when executing the following
>code:
>
>#include <stdio.h>
>
>main()
>{
>	char array[32000];
>
>	printf("\nHello, world!\n");
>}

Here's why it bombs:
array is a local variable to the function main.  array is allocated on the
stack when main is entered.  This allocation happens before the printf, and
hoses the machine since 32000 bytes is really an awful lot to ask from the
machine as local variable space for a single function, since the limit imposed
by the compiler is 32K.  If you REALLY feel you have to do this, try making
your array static (which will limit you to only another 767 bytes of global
and static data), which puts it in global space.  Or (I know this isn't what
you want to hear) allocate it on the fly from the heap.  The heap will
probably be much much larger than the stack.  Remember the purpose of local
variables: small amounts of storage for variables you will need temporarily
that can be used re-entrantly (otherwise recursion won't work as well as you'd
like it to).

If you want to see death in a C environment, try the following program on a
variety of machines:

#include <stdio.h>

int deathcount = 0;

death()
{
	char a[1024]; /* 1K allocated on the stack */
	a[0] = a[0]; /* prevent a from being linked out by an optimizer */
	printf("%dK"\n", ++deathcount);
	fflush(stdout);
	death();
}

main()
{
	death();
}

On a Sun 3/80 with all the wonders of UNIX memory management, it can only cope
with 2036K (!!) before it core dumps.  Try it on a Mac to see what it's limits
are (I can't, since I don't have a Mac anymore (sniff)) under Think C.

Steve Hawley
hawley@adobe.com
-- 
"I can always telephone, but I can't tell it much."
	-Roy Blount