Reference to freed storage

Memory is accessed after it has been deallocated.

This is a serious error because the storage being accessed could have been reused. Therefore, a read could deliver an unpredictable value and a write could corrupt another variable or the entire heap. This condition is also called a "stale pointer" error, indicating that a pointer has been used after it has become invalid or stale.

ID	Code Location	Description
1	Bad memory access	The place where the memory was accessed

Example

          
#include <stdio.h>

int main(int argc, char **argv)
{
    int *p, *q;
    p = (int *)malloc(4);
    *p = 1;
    free(p);
    q = (int *)malloc(4);
    *q = 2;
    *p = 3; // error here: can't use p after it was freed
    printf("*q = %d\n", *q); // Will this print "q = 2" or "q = 3"?
}