Pointers defined using specific data type cannot hold the address of the some other type of variable i.e., it is incorrect in C++ to assign the address of an integer variable to a pointer of type float.

Example:

float *f; //pointer of type float
int i;  //integer variable
f = &i; //compilation error

The above problem can be solved by general purpose pointer called void pointer.

Void pointer can be declared as follows:

 
void *v // defines a pointer of type void

The pointer defined in this manner do not have any type associated with them and can hold the address of any type of variable.

Example:

void *v; 
int *i;
int ivar;
char chvar;
float fvar;
v = &ivar; // valid
v = &chvar; //valid
v = &fvar; // valid
i = &ivar; //valid
i = &chvar; //invalid
i = &fvar; //invalid

The post what is Void Pointer? first appeared on Student Projects.

In many applications memory is allocated for holding data objects. After using these objects, tha aplication will de-allocate this memory so that the memory can be re-used. In some cases the alications may use a pointer to an object whose memory is already de-allocated. This may lead to application crash or an unpredictable behavior.

scenarios which leads to dangling pointer

1. Application makes use of a object after it has been released, and there by access to an invalid memory location.
2. A function returns a pointer to one of its local variables, and since this local variable is defined only fro the function, the pointer becomes invalid once the function ends.

The most common result of this bug is the crash of the application or its running thread.

Examle 1:

#include "stdlib.h"
 
void func()
{
    char *dp = malloc(A_CONST);
    /* ... */
    free(dp);         /* dp now becomes a dangling pointer */
    /* ... */
}

Example 2:

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

Example 3:

#include "stdio.h"

int *call();
void main(){

int *ptr;
ptr=call();

fflush(stdin);
printf("%d",*ptr);
}

int * call(){

int x=25;
++x;

return &x;
}

The post What is dangling pointer? first appeared on Student Projects.