Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!apple!bloom-beacon!adam.pika.mit.edu!scs
From: scs@adam.pika.mit.edu (Steve Summit)
Newsgroups: comp.lang.c
Subject: Re: malloc & tc.
Keywords: malloc, turboc
Message-ID: <11399@bloom-beacon.MIT.EDU>
Date: 13 May 89 19:20:34 GMT
References: <8283@techunix.BITNET>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: scs@adam.pika.mit.edu (Steve Summit)
Lines: 30

In article <8283@techunix.BITNET> ssreefc@techunix.BITNET (florin coter) writes:
>        extern char a[1000][50];        /* !!! */
>                if( ( *p=malloc( (unsigned)30000 ) ) == NULL )
>                        puuts( "no space" );

I suspect that the "*p=" and "puuts" are typos; I suspect that
the "extern" on the declaration of a is not.  Being external,
this declaration is what is called a "declaring instance," not a
"defining instance."  It allocates no space.  Since a is not
used, the declaration is essentially discarded, ~50K is not set
aside, and sufficient memory remains to satisfy the malloc(30000)
request.  (If a were used, you would get an "undefined symbol"
error at link time, noting the absence of a defining instance.)

Malloc is an extremely important and oft-used routine.  Although
subtle bugs are occasionally noted in new implementations,
it is quite unlikely that a non-NULL pointer to in-use
memory could ever be returned during an out-of-memory condition
(or under any other circumstances, for that matter).  Malloc has
to return NULL when there's no memory.  That's its job.

                                            Steve Summit
                                            scs@adam.pika.mit.edu

P.S. Please be very careful about typos in source postings,
     incorporating the C source file directly into your text
     editor while composing the message, if possible.  Otherwise
     people may correct your typos and overlook the real problem
     (which I don't claim to have discovered either, because the
     posting is still a bit sketchy).