Heap Error

[CMR]

Hello all

I'm writing a Console application that supports MFC. Basically, it scans through a text file and updates a datbase with the data in the file. Pretty simple stuff - but I have a strange problem which I can only assume is related to memory management.
I'm getting a heap error when I try to use CString::Right() - HEAP: Free Heap block 4b5d408 modified at 4b5d47c after it was freed.

I'm sure it isn't CString that's the problem here as when I comment this line out the error moves elsewhere. (it just seems to move to the next instruction that involves allocating memory).
The weird thing is, the program will run for a bit and then fail - i.e. it will process the first three or so lines of my text file but then gives a "user breakpoint" error and the debug window will show the heap error.

Any ideas?

Thanks in advance for any help

CMR

 

[LazyMe]

It menas that you have written beyind some bounds in allocated memory.
Greetings,
Rick

 

[CMR]

Found the problem:

I had two CString objects, one local and one global. I was making the global one equal to the local one which waas causing problems when the local function went out of scope.
Apparently, CString "=" doesn't copy each character as you might expect it to; it creates a pointer to the original CString for the copy so when the original goes out of scope it causes memory allocation problems.

I'll try to avoid making that mistake again....

CMR

 

[sskumar]

Actually i can't get the problem. if possible paste the sample code for explaining.

i tried like this

#include "afx.h"
CString xx;
void fn1();
void main(void){
fn1();
if(xx.IsEmpty())
cout<<&quot;Empty&quot;;
else
cout<<xx;
}

void fn1(){
CString x = &quot;std&quot;;
xx = x;
}

 

[CMR]

I don't think it's as simple as that. The problem seems to occur not when you copy the string, but when you next try to allocate memory - i.e. when you use &quot;new&quot; of something that dynamically allocates memory.
I wasn't able to tell exactly which instruction it was falling over at (it was buried deep in a .lib file I think) but when I declared all my CStrings as local rather than some local, some global it fixed the problem.

Thanks for taking the time to look at it anyway

CMR