Why this code is not causing memory leak?

Question

I wanted to simulate memory leak in my application. I write following code, and tried to see in perfmon.

int main()
{
    int *i;
    while(1)
    {

        i = (int *) malloc(1000);

        //just to avoid lazy allocation
        *i = 100;

        if(i == NULL)
        {
            printf("Memory Not Allocated\n");
        }

        Sleep(1000);
    }
}

When I see used memory in Task Manager, it is fluctuate between 52K and 136K, but not going beyond that. Means, somethings it shows 52K and sometimes 136K, I do not understand how this code once goes to 136K, coming back to 52K, and not going beyond that.

I tried to use perfmon, but not able to exactly what to see in perfmon, snapshot of counters,

Please suggest how to simulate memory leak and how to detect it.

Answer 1

Strictly, a memory leak is a bit context dependent: something in your program keeps allocating memory over time and not freeing it, when it should have been freed.

You code produces a "leak" on each subsequent pass through the while loop, because your program loses knowledge of a previously allocated pointer at that point. This is only visible by inspection however in this case; from the code posted it looks more like you are actually doing, albeit very slowly, is attempting to create a memory stress situation.

To 'find' a leak without inspection you need to run a tool like valgrind (Unix/Linux/OSX) or in Visual Studio enable allocation tracing with the DEBUG_NEW macro and view the output using a debugger.

If you really want to stress memory in a hurry, allocate 1024 x 1024 x 1024 bytes at a time...