Dangling and Wild Pointers - Embedded C Programming Frequently Asked Interview Questions

Dangling Pointer :

Dangling pointers in computer programming are pointers that do not point to a valid object of the appropriate type. Dangling pointers arise when an object is deleted or deallocated, without modifying the value of the pointer, so that the pointer still points to the memory location of the deallocated memory.
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Examples of Dangling Pointers

int main()
{

int *p;
p = (int *) malloc (sizeof (int));

free(p);
*p=10;

}

In the above piece of code we are using *p after we free the memory to it.
Such usage is called dangling pointer usage.

int main()
{

int *p = NULL;
{
int a = 10;
p = &a;
}
/*address of a is out of scope and pointer p is now called the dangling pointer, we should initialize the p to NULL before coming out or initialize the pointer to some known value before using it again*/
…
}

int* fun1()
{
int a = 10;
return(&a); /*in this line we are returning the pointer of variable ‘a’ which is out scope.*/
}

Wild Pointers:

Wild pointers are created by omitting necessary initialization prior to first use. Thus, strictly speaking, every pointer in programming languages which do not enforce initialization begins as a wild pointer. This most often occurs due to jumping over the initialization, not by omitting it. Most compilers are able to warn about this.

{

int* a;

/* a is wild pointer, it is not initialized and it may have some garbage value*/

}

correct way is
{
int* a = NULL;
}