Message-Id: <9707071300.AA17833@sun4nl.NL.net>
Date: Mon, 7 Jul 1997 12:22:00 +0200
From: Rob den Boer <rob DOT den DOT boer AT derijke DOT nl>
Subject: AW: Memory Leak patch Please.
To: b2042026 <b2042026 AT est DOT fib DOT upc DOT es>
Cc: djgpp <djgpp AT delorie DOT com>
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Hi all,


The attached file MEMCHK.ZIP contains the memchk.c source.
With this you can track down memory bugs, like not freeing pointers,   
using wrong pointers etc.

It's adapted from an old piece of code published in DDJ back in the 90's,   
and made it work with DJGPP.

You can use it as follows:
1. after your regular #include's add:
#define MEM_DEBUG 1
#include "memchk.c"


2. first thing in your main:
#ifdef MEM_DEBUG
 mem_check_init();
#endif

3. run your program!
4. check the file MEMCHK.LOG

If all is well, the logfile will show something like this:
Summary:
Total allocated memory  : 0 bytes
Memory usage maximum    : 11880 bytes
Number of pointers used : 70
total Bitmaps           : 861448 bytes, 85 x

The 'total' allocated should be 0, otherwise you have a memory leak. You   
will see when things go wrong. Checks are done for:

1. malloc calls returning NULL pointers
2. multiple allocating of the same pointer
3. freeing a null pointer
4. freeing a pointer multiple times
5. bounds check (not 100% proof, see below)

Use #define MEM_DEBUG_ALL to see all allocations/free's in your program.
remove the MEM_DEBUG defines when your programs works great and you want   
to compile the final version, this leaves out all checking code.


How does it work?
The init function installs an atexit function, which does the end   
reporting.
This code keeps an administration of all malloc/calloc/free calls, and   
keeps track of memory. To 'catch' the malloc/free calls in your program,   
memchk.c #defines malloc/calloc/free and replaces them with it's own   
custom versions.
For each allocation there's a MEMHDR structure, which is linked into a   
list.
Bounds checking is done by putting a magic value before and after the   
allocated memory area. Usually when you move outside the allocated memory   
area, you will touch the magic values, and this will be detected. It's   
not 100% proof, because you can skip them, but it's neat when it's   
detected.

I quickly re-wrote this for my own use, because I had the same problems   
as you. Therefore it's not finished yet, like the strdup function doesn't   
work yet, and it doesn't work on multiple sourcefiles yet. I have to   
split it into a .c/.h for that.
The BITMAP thing is for Allegro, it only counts how much was used for   
bitmaps. (it's no use tracking them down, because Allegro free's them on   
exit).


regards
Rob den Boer

[[ MEMCHK.ZIP : 2101 in MEMCHK.ZIP ]]  

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