C++ Void Pointer

A void pointer is a general-purpose pointer that can hold the address of any data type, but it is not associated with any data type.

Syntax of void pointer

In C++, we cannot assign the address of a variable to the variable of a different data type. Consider the following example:

int *ptr;  // integer pointer declaration
float a=10.2; // floating variable initialization
ptr= &a;  // This statement throws an error.

In the above example, we declare a pointer of type integer, i.e., ptr and a float variable, i.e., 'a'. After declaration, we try to store the address of 'a' variable in 'ptr', but this is not possible in C++ as the variable cannot hold the address of different data types.

Let's understand through a simple example.

#include <iostream.h>
using namespace std;
int main()
{
    int *ptr;
    float f=10.3;
    ptr = &f; // error
    std::cout << "The value of *ptr is : " <<*ptr<< std::endl;
    return 0;
}

In the above program, we declare a pointer of integer type and variable of float type. An integer pointer variable cannot point to the float variable, but it can point to an only integer variable.

Output

C++ has overcome the above problem by using the C++ void pointer as a void pointer can hold the address of any data type.

Let's look at a simple example of void pointer.

#include <iostream>
using namespace std;
int main()
{
  void *ptr;   // void pointer declaration
  int a=9;   // integer variable initialization
  ptr=&a;   // storing the address of 'a' variable in a void pointer variable.
  std::cout << &a << std::endl;
  std::cout << ptr << std::endl;
  return 0;
}

In the above program, we declare a void pointer variable and an integer variable where the void pointer contains the address of an integer variable.

Output

Difference between void pointer in C and C++

In C, we can assign the void pointer to any other pointer type without any typecasting, whereas in C++, we need to typecast when we assign the void pointer type to any other pointer type.

Let's understand through a simple example.

In C,

#include <stdio.h>
int main()
{
   void *ptr; // void pointer declaration
   int *ptr1;  // integer pointer declaration
   int a =90;  // integer variable initialization
   ptr=&a; // storing the address of 'a' in ptr
   ptr1=ptr; // assigning void pointer to integer pointer type.
   printf("The value of *ptr1 : %d",*ptr1);
   return 0;
}

In the above program, we declare two pointers 'ptr' and 'ptr1' of type void and integer, respectively. We also declare the integer type variable, i.e., 'a'. After declaration, we assign the address of 'a' variable to the pointer 'ptr'. Then, we assign the void pointer to the integer pointer, i.e., ptr1 without any typecasting because in C, we do not need to typecast while assigning the void pointer to any other type of pointer.

Output

In C++,

#include <iostream>
using namespace std;
int main()
{
  void *ptr; // void pointer declaration
  int *ptr1; // integer pointer declaration
  int data=10; // integer variable initialization
  ptr=&data;  // storing the address of data variable in void pointer variable
  ptr1=(int *)ptr; // assigning void pointer to integer pointer
  std::cout << "The value of *ptr1 is : " <<*ptr1<< std::endl;
  return 0;
}

In the above program, we declare two pointer variables of type void and int type respectively. We also create another integer type variable, i.e., 'data'. After declaration, we store the address of variable 'data' in a void pointer variable, i.e., ptr. Now, we want to assign the void pointer to integer pointer, in order to do this, we need to apply the cast operator, i.e., (int *) to the void pointer variable. This cast operator tells the compiler which type of value void pointer is holding. For casting, we have to type the data type and * in a bracket like (char *) or (int *).

Output