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From: papke@dicomed.UUCP (Kurt Papke)
Newsgroups: net.micro.pc
Subject: Re: Problems with Microsoft C V 3.0 memory routines
Message-ID: <649@dicomed.UUCP>
Date: Thu, 14-Nov-85 08:23:19 EST
Article-I.D.: dicomed.649
Posted: Thu Nov 14 08:23:19 1985
Date-Received: Sat, 16-Nov-85 09:38:30 EST
References: <279@infinet.UUCP>
Reply-To: papke@dicomed.UUCP (Kurt Papke)
Organization: DICOMED Corp., Minneapolis
Lines: 32

In article <279@infinet.UUCP> cgf@infinet.UUCP (Chris Faylor) writes:
>{}
>Has anyone out there noticed any problems with the realloc routine
>distributed with Microsoft C?  It seems to sometimes leave garbage
>in the middle of a reallocated block of memory if the newly malloc'ed
>block overlaps the old.

I have used the realloc() routine quite a bit and have never experienced
the problem you describe.

>Looking at the code, it seems pretty obvious that there will be times
>when this will definitely happen.  It will always fail if you try
>to increase the size of a block from, say, 10 bytes to 16 bytes, and
>there are 6 free bytes immediately preceding the original ten.
>What happens is that realloc first frees the block it is trying to
>expand, then malloc sets aside the only available 16 bytes, placing
>a memory size header in the middle of the original 10 byte block.
>Then realloc copies the old block, header and all, up 6 bytes.

Could be.  How do you know this without the sources to the run-time
library ??

>In general, it seems that malloc does not behave well if you have
>the misfortune of running out of memory.  I have not completely
>corroborated it, but it looks like a pointer somewhere gets
>screwed up.  After returning a NULL (indicating that there isn't
>enough contiguous memory for the request) it appears that it will
>sometimes start allocating new memory over previously allocated blocks.
>Anybody else seen this?

No, although most of the code I've written with 3.0 has no choice but
to roll over and die when it runs out of heap !!