Difference Between Reference Variable and Pointer Variable

Which is preferred, Passing by Pointer Vs Passing by Reference in C++?

A reference is the same object, just with a different name and a reference must refer to an object. Since references can’t be NULL, they are safer to use.

A pointer can be re-assigned while a reference cannot, and must be assigned at initialization only.
The pointer can be assigned NULL directly, whereas the reference cannot.
Pointers can iterate over an array, we can use increment/decrement operators to go to the next/previous item that a pointer is pointing to.
A pointer is a variable that holds a memory address. A reference has the same memory address as the item it references.
A pointer to a class/struct uses ‘->’ (arrow operator) to access its members whereas a reference uses a ‘.’ (dot operator)
A pointer needs to be dereferenced with * to access the memory location it points to, whereas a reference can be used directly.

Example: The following C++ program demonstrates the differences.

C++

// C++ program to demonstrate differences
// between pointer and reference
#include <iostream>
using namespace std;
 
struct demo {
    int a;
};
 
int main()
{
    int x = 5;
    int y = 6;
    demo d;
 
    int* p;
    p = &x;
    p = &y; // 1. Pointer reinitialization allowed
 
    int& r = x;
    // &r = y;                 // 1. Compile Error
 
    r = y; // 1. x value becomes 6
 
    p = NULL;
    // &r = NULL;             // 2. Compile Error
 
    // 3. Points to next memory location
    p++;
 
    // 3. x values becomes 7
    r++;
 
    cout << &p << " " << &x << '\n'; // 4. Different address
    cout << &r << " " << &x << '\n'; // 4. Same address
 
    demo* q = &d;
    demo& qq = d;
 
    q->a = 8;
    // q.a = 8;                 // 5. Compile Error
    qq.a = 8;
    // qq->a = 8;             // 5. Compile Error
 
    // 6. Prints the address
    cout << p << '\n';
 
    // 6. Print the value of x
    cout << r << '\n';
 
    return 0;
}

Output

0x7ffdfc7bead8 0x7ffdfc7bead4
0x7ffdfc7bead4 0x7ffdfc7bead4
0x4
7

Passing By Pointer vs Passing By Reference in C++

In C++, we can pass parameters to a function either by pointers or by reference. In both cases, we get the same result. So, what is the difference between Passing by Pointer and Passing by Reference in C++?

Let’s first understand what Passing by Pointer and Passing by Reference in C++ mean: