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From: dmb@wam.umd.edu (David M. Baggett)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Problem with my C program [a few general hints about malloc]
Message-ID: <1991Apr22.014758.3846@wam.umd.edu>
Date: 22 Apr 91 01:47:58 GMT
References: <1991Apr21.210056.5685@ccu.umanitoba.ca>
Sender: usenet@wam.umd.edu (USENET Posting)
Organization: University of Maryland at College Park
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In article <1991Apr21.210056.5685@ccu.umanitoba.ca> umochock@ccu.umanitoba.ca (Russell Ochocki) writes:
>
>I try to Malloc a buffer equal to the size of the file being copyied.  Then I
>do a Fread from the source file, prompt the user to swap disks, fopen the
>destination file, and Fwrite the contents of the buffer.  And, fclose both
>files.  Note: I needed to use Malloc, Fread, and Fwrite since I required long
>ints (not the short expected by malloc, fread, and fwrite).

Although this isn't what you were asking about, I think it's worth
mentioning for the benefit of others who are just starting out:

If you want to allocate more memory than can be specified in an unsigned int,
use calloc.  It takes two parameters which are multiplied together to get
the size of the requested block.  To allocate 128K:

	p = calloc(128, 1024);

As a bonus the memory you get is also cleared.  You could write your own
replacement for Malloc as follows:

char *
my_Malloc(size)
	register long	size;
{
	register unsigned	hi, lo;

	hi = (unsigned) (size >> 16);
	lo = (unsigned) (size & 0x0000FFFF);

	return calloc(hi, lo);
}

(This assumes that a long is 32 bits and an unsigned int is 16, which is
not portable, so it's best to use calloc directly.)

In general it is VERY WISE to avoid using the bios Malloc and Free and
use the malloc, calloc, and free provided with your compiler of
choice.  The bios Malloc has bugs (some still remain for historical
reasons) and is quite ideosyncratic.  Sozobon's malloc and calloc (in
dlibs.a) work quite well, although one caveat to Sozobon users is that
the malloc routines can only manage 1 Meg of memory.  A trivial change
to the dlibs source file malloc.c fixes this, fortunately.

Also, assuming you were using fread and fwrite, you would have to
be sure to specify "b" in the flags ("b" for "binary") to prevent
automatic conversion of CR to CR/LF.

Dave Baggett
dmb%wam.umd.edu@uunet.uu.net