C++ References and Pointers

Hi everyone, inside this article we will see about C++ References and Pointers.

In C++, both references and pointers are used to indirectly access a variable or object. However, there are some differences between the two.

A reference is essentially an alias for a variable. It provides an alternative name for an existing variable, and allows us to manipulate the variable indirectly. Once a reference is initialized to a variable, it cannot be re-bound to another variable.

A pointer, on the other hand, is a variable that stores the memory address of another variable. It allows us to indirectly access the value of a variable by manipulating its memory address. Unlike a reference, a pointer can be re-assigned to point to a different memory location.

1. Call-By-Value
2. Call-By-Reference with a Pointer Argument
3. Call-By-Reference with a Reference Argument

Example #1

Here is an example program that demonstrates the use of both references and pointers in C++:

#include <iostream>
using namespace std;
// Pass-by-Value
int square1(int n)
{
  cout << "address of n1 in square1(): " << &n << "\n";
  n *= n;
  return n;
}
// Pass-by-Reference with Pointer Arguments
void square2(int *n)
{
  cout << "address of n2 in square2(): " << n << "\n";
  *n *= *n;
}
// Pass-by-Reference with Reference Arguments
void square3(int &n)
{

  cout << "address of n3 in square3(): " << &n << "\n";
  n *= n;
}
void example()
{
  // Call-by-Value
  int n1 = 8;
  cout << "address of n1 in main(): " << &n1 << "\n";
  cout << "Square of n1: " << square1(n1) << "\n";
  cout << "No change in n1: " << n1 << "\n";

  // Call-by-Reference with Pointer Arguments
  int n2 = 8;
  cout << "address of n2 in main(): " << &n2 << "\n";
  square2(&n2);
  cout << "Square of n2: " << n2 << "\n";
  cout << "Change reflected in n2: " << n2 << "\n";

  // Call-by-Reference with Reference Arguments
  int n3 = 8;
  cout << "address of n3 in main(): " << &n3 << "\n";
  square3(n3);
  cout << "Square of n3: " << n3 << "\n";
  cout << "Change reflected in n3: " << n3 << "\n";
}
// Driver program
int main()
{
  example();
}

Output

address of n1 in main(): 0x7fff1518902c
Square of n1: address of n1 in square1(): 0x7fff1518900c
64
No change in n1: 8
address of n2 in main(): 0x7fff15189030
address of n2 in square2(): 0x7fff15189030
Square of n2: 64
Change reflected in n2: 64
address of n3 in main(): 0x7fff15189034
address of n3 in square3(): 0x7fff15189034
Square of n3: 64
Change reflected in n3: 64

Example #2

Here is another example program that demonstrates the use of both references and pointers in C++:

#include <iostream>

using namespace std;

int main() {
  int value = 10;        // An integer value

  int &ref = value;      // A reference to an integer

  int *ptr = &value;     // A pointer to an integer

  cout << "The value of the integer is " << value << endl;
  cout << "The value of the integer through the reference is " << ref << endl;
  cout << "The value of the integer through the pointer is " << *ptr << endl;

  value = 20;            // Update the value of the integer

  cout << "The value of the integer is " << value << endl;
  cout << "The value of the integer through the reference is " << ref << endl;
  cout << "The value of the integer through the pointer is " << *ptr << endl;

  ref = 30;              // Update the value of the integer through the reference

  cout << "The value of the integer is " << value << endl;
  cout << "The value of the integer through the reference is " << ref << endl;
  cout << "The value of the integer through the pointer is " << *ptr << endl;

  ptr = nullptr;         // Set the pointer to null

  return 0;
}

Output

The value of the integer is 10
The value of the integer through the reference is 10
The value of the integer through the pointer is 10
The value of the integer is 20
The value of the integer through the reference is 20
The value of the integer through the pointer is 20
The value of the integer is 30
The value of the integer through the reference is 30
The value of the integer through the pointer is 30

In this program, we first declare an integer variable value, and then create a reference ref that is initialized to value, and a pointer ptr that points to the memory location of value.

We then print out the values of value, ref, and *ptr (which is equivalent to the value of value), and update the value of value and ref. We print out the values again, and observe that the values of value, ref, and *ptr are all updated.

Finally, we set the value of ptr to nullptr (which is a null pointer), indicating that it no longer points to any memory location.

Note that in the program, the syntax for using references and pointers is different. To declare a reference, we use the & symbol after the variable name, while to declare a pointer, we use the * symbol before the variable name. To access the value of a variable through a reference, we simply use the reference variable name, while to access the value through a pointer, we use the * symbol before the pointer variable.

We hope this article helped you to understand about C++ References and Pointers in a very detailed way.

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