Uninitialized memory blocks in VC++

Question

As everyone knows, the Visual C++ runtime marks uninitialized or just freed memory blocks with special non-zero markers. Is there any way to disable this behavior entirely w

Answer 1

If it's working in release mode, it's because of shear luck.

Mike B is right to assume that the debug fix is hiding a bug. In release mode, a pointer is being used that has been freed but not set to NULL, and the memory it points to is still "valid". At some point in the future, memory allocations will change, or the memory image will change, or something will cause the "valid" memory block to become "invalid". At that point, your release build will start failing. Switching to debug mode to find the problem will be useless, because the debug mode has been "fixed".

I think we call all agree that the following code shouldn't work.

char * p = new char[16];     // 16 bytes of random trash
strcpy(p, "StackOverflow");  // 13 characters, a '\0' terminator, and two bytes of trash
delete [] p;                 // return 16 bytes to the heap, but nothing else changes;

if (p != NULL)               // Why would p be NULL?  It was never set to NULL
    ASSERT(p[0] == 'S');     // In debug, this will crash, because p = 0xfeeefeee and 
                             // dereferencing it will cause an error.
                             // Release mode may or may or may not work, depending on
                             // other memory operations

As just about every other poster has said, pointers should be set to NULL after calling delete. Whether you do it yourself or use boost or some other wrapper or even the macro in this thread is up to you.