From: Damian Yerrick <Bullcr_pd_yerrick AT hotmail DOT comRemoveBullcr_p>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Unstandard mallocation needed
Organization: Pin Eight Software  http://pineight.8m.com/
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NNTP-Posting-Date: Sun, 25 Jun 2000 15:50:01 GMT
Distribution: world
Date: Sun, 25 Jun 2000 15:50:01 GMT
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

On Sun, 25 Jun 2000 13:24:51 +0300 (IDT), Eli Zaretskii
<eliz AT is DOT elta DOT co DOT il> wrote:

>
>On Sun, 25 Jun 2000, Martin Nilsson wrote:
>
>> Q:  So can I query the malloc package to find out how big
>> an allocated block is?
>> 
>> A:  Unfortunately, there is no standard or portable way.
>> 
>> but I would like to do it anyway, with DJGPP. None of the
>> memory allocation routines listed in info.exe seem to fit.
>> Does somebody know how to do it? It would be extra nice if
>> the solution was somwhat portable to the GNU GCC compiler.
>
>As the C FAQ tells you: there's no portable solution.  You can hack the 
>sources of the DJGPP's implementation of malloc (it's in djlsr203.zip), 
>if you really need it, but that would be not portable to any other 
>library.
>
>Many people want these features because they want to detect memory leaks 
>in their programs.  If that's your reason as well, there are special 
>packages out there for this purpose; the DJGPP FAQ mentions several of 
>them in section 22.4.
>
>> p = realloc(p, 50);    /* saving the contents of bytes
>> 0..49, freeing bytes 50..99 */
>> 
>> thus doing a nifty "slicing" operation without having to
>> copy anything. It would be nice to also be able to do the "opposite"
>> operation, i e freeing the *first* n bytes,
>> like this:
>> 
>> byte *p = malloc(100);
>> . . .
>> 
>> p = free_the_first_n_bytes(p, 35);
>> /* p now is old p + 35;
>> bytes 0..34 are freed */
>
>You can't, not in the current implementation of malloc, anyway.
>It stores internal info about the allocated block in a few bytes
>immediately preceding and following the allocated block.

I'd just use a memmove() then a realloc() until somebody (hint hint)
submits a patch that allows this.  However, it probably will be able
only to chop off multiples of 8 bytes from the start of a block.

-- 
Damian Yerrick
"I refuse to listen to those who refuse to listen to reason."
See the whole sig: http://www.rose-hulman.edu/~yerricde/sig.html

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