Mail Archives: djgpp/1997/07/07/09:31:07
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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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