Pointers and References in C++

In C++, pointers and references are both mechanisms used to deal with memory, memory addresses, and data in a program. Pointers are used to store the memory address of another variable, whereas references are used to create an alias for an already existing variable.

Pointers in C++

Pointers in C++ are a symbolic representation of addresses. They enable programs to simulate call-by-reference and create and manipulate dynamic data structures.

• Pointers store the address of variables or a memory location. 
• Can be reassigned to point to another variable
• Can be nullptr
• Requires dereferencing to access the value
• Has its own memory address

Syntax

datatype *var_name;

#include <iostream>
using namespace std;

int main(){
    int x = 10; // variable declared
    int* myptr; // pointer variable

    // storing address of x in pointer myptr
    myptr = &x;

    cout << "Value of x is: ";
    cout << x << endl;

    // print the address stored in myptr pointer variable
    cout << "Address stored in myptr is: ";
    cout << myptr << endl;

    // printing value of x using pointer myptr
    cout << "Value of x using *myptr is: ";
    cout << *myptr << endl;

    return 0;
}

Value of x is: 10
Address stored in myptr is: 0x7ffd2b32c7f4
Value of x using *myptr is: 10

Explanation: The above program declares an integer variable 'x' initialized with value 10 and a pointer variable named 'myptr'. The memory address of x is assigned to myptr. Then it prints the value of x, the address stored in myptr, and the value of x obtained by dereferencing the pointer myptr.

References in C++

When a variable is declared as a reference, it becomes an alternative name for an existing variable. A variable can be declared as a reference by putting '&' in the declaration. There are 3 ways to pass C++ arguments to a function: 

• call-by-value
• call-by-reference with a pointer argument
• call-by-reference with a reference argument

#include <iostream>
using namespace std;

int main(){
    int y = 10;

    // ref is a reference to x.
    int& myref = y;

    // changing value of y to 20
    y = 30;
    cout << "value of y is " << y << endl;
    cout << "value of myref after change in value of y is: "
         << myref << '\n';

    return 0;
}

value of y is 30
value of myref after change in value of y is: 30

Explanation: The above program demonstrates the use of references. First, it declares an integer variable 'y' and then creates reference 'myref' which is an alias to y. Changing the value of y also changes the value of myref which can be seen after printing values of both y and myref.

Pointers vs References

Below are key difference between pointers and references in C++ based on their behavior, usage, and memory handling.