Dangling pointers arise when an object is deleted or de-allocated, without modifying the value of the pointer, so that the pointer still points to the memory location of the de-allocated memory. In short pointer pointing to non-existing memory location is called dangling pointer.
Example:
#include<stdlib.h>
{
char *ptr = malloc(Constant_Value);
.......
.......
.......
free (ptr); /* ptr now becomes a dangling pointer */
}