Re: Unable to free malloc'd ptr
"Jason Pawloski" <jpawloski@gmail.com> wrote in message
news:1182377203.259749.209000@c77g2000hse.googlegroups.com...
First of all, I need to apolgoize; I am not a programmer and its been
years since I last programmed something so this is probably a very
simple question. For work, I have to write a simulation.
[...]
nr1 = function2([parameter]);
Now when I try to free it later in my first function (the one that
calls function2), I get an MSVC++ error. The exact wording is:
[...]
DAMAGE: after Normal block (#46) at 0x00431D80
[...]
You have corrupted some adjacent blocks of memory wrt area in memory that
'nr1' points to. This corruption probably screwed up some of the memory
allocators internal bookkeeping structures. Well, here is a __very crude__
method you can try for tracking down "something to do" with the reason why
your experiencing memory corruption:
_________________
int *dropreel(int *list,int size,int position)
{
int *nl = NULL;
/*Put the index in range */
while(position > size-1) position = position - size;
while(position < 0) position = position + size;
nl = malloc(sizeof(int)*(size-1));
if(nl == NULL)
printf("WARNING!! NO MEMORY!\n");
// return 0;
// }
//D1: free(nl);
memset(nl,0,sizeof(int)*(size-1));
//D2: free(nl);
if(position != size-1)
nl[0] = list[size-1];
//D3a: free(nl);
else
nl[0] = list[size-2];
//D3b: free(nl);
memcpy(&nl[1],list,sizeof(int)*(position));
//D4: free(nl);
memcpy(&nl[position+1],&list[(position+1)],sizeof(int)*(size-position-1));
//D5: free(nl);
return nl;
}
_________________
Start by uncommenting line D1 and then step through the code and see if D1
crashes... After that just re-comment D1 and uncomment D2, and step through
the code again to validate that D2 works... Repeat the pattern for all of
the lines prefixed with D... If they all work, then your problem probably
has something to do with corruption in the memory that the 'list' parameter
points. If that is the case then it possibly could be effecting the
integrity of the memory blocks either pointed to by 'nl', or some
adjacent/contiguous ones...
The allocator has detected corruption, and you need to take a step back, and
start to examine your code in great detail. When your debugging and stepping
through your code line by line, play close attention to watched variables...
If you do a memcpy on a piece of memory, and you notice that one of your
watched variables that has nothing to do with the memcpy target changes,
well, that's a major red flag!
Happy bug hunting!
;^0