Dangling Memory

Dangling Memory

Dangling memory is a memory location allocated to an object that cannot be referenced any more.

It is normally a result of a logical mistake in the code.

For example, while we are in a function, we may allocate arrays dynamically, use them and when we exit the function, the allocated memory will not be de-allocated there by leading to a dangling memory problem.

A pointer pointing to a non existing memory location is called a “Dangling Pointer”.

Dangling pointer is the pointer; when an object is de-allocated without modify the value of the pointer, even though the pointer still points to the memory location of the de-allocated memory. This may lead to an application crash or an unpredictable behaviour:

Scenario that cause dangling pointer:

Application makes use of an object after it has been released, and there by accessing to an invalid memory location.

A function returns a pointer to one of its local variables, and since this local variable is defined only from the function, the pointer becomes invalid once the function ends.

Example:

char *dp =NUL                  { char c; dp = &c; } // c falls out of scope //dp is now a dangling pointer

dp 1001

NULL Pointer in C:

A pointer that is assigned NULL is called a null pointer and this is done at the time of a variable declaration.

Assign a NULL value to a pointer variable, in case we do not have an exact address to be assigned. It is a constant, with a value of zero defined in standard libraries.

Example

#inlcude<stdio.h>

int main()

{

int *pr = NULL;

printf(“The value of pr is: %x\n”, &pr);

return 0;

}

OUTPUT: The value of pr is fff4