Return by reference in C++ with Examples

Pointers and References in C++ held close relation with one another. The major difference is that the pointers can be operated on like adding values whereas references are just an alias for another variable.

• Functions in C++ can return a reference as it’s returns a pointer.
• When function returns a reference it means it returns a implicit pointer.

Return by reference is very different from Call by reference. Functions behaves a very important role when variable or pointers are returned as reference.

See this function signature of Return by Reference Below:

dataType& functionName(parameters);
where,
dataType is the return type of the function,
and parameters are the passed arguments to it.

Below is the code to illustrate the Return by reference:

CPP

// C++ program to illustrate return by reference
#include <iostream>
using namespace std;

// Function to return as return by reference
int& returnValue(int& x)
{

    // Print the address
    cout << "x = " << x
         << " The address of x is "
         << &x << endl;

    // Return reference
    return x;
}

// Driver Code
int main()
{
    int a = 20;
    int& b = returnValue(a);

    // Print a and its address
    cout << "a = " << a
         << " The address of a is "
         << &a << endl;

    // Print b and its address
    cout << "b = " << b
         << " The address of b is "
         << &b << endl;

    // We can also change the value of
    // 'a' by using the address returned
    // by returnValue function

    // Since the function returns an alias
    // of x, which is itself an alias of a,
    // we can update the value of a
    returnValue(a) = 13;

    // The above expression assigns the
    // value to the returned alias as 3.
    cout << "a = " << a
         << " The address of a is "
         << &a << endl;
    return 0;
}

Output:

x = 20 The address of x is 0x7fff3025711c
a = 20 The address of a is 0x7fff3025711c
b = 20 The address of b is 0x7fff3025711c
x = 20 The address of x is 0x7fff3025711c
a = 13 The address of a is 0x7fff3025711c

Explanation:

Since reference is nothing but an alias(synonym) of another variable, the address of a, b and x never changes.

Note: We should never return a local variable as a reference, reason being, as soon as the functions returns, local variable will be erased, however, we still will be left with a reference which might be a security bug in the code.

Below is the code to illustrate the Return by reference:

C++

// C++ program to illustrate return
// by reference
#include <iostream>
using namespace std;

// Global variable
int x;

// Function returns as a return
// by reference
int& retByRef()
{
    return x;
}

// Driver Code
int main()
{
    // Function Call for return
    // by reference
    retByRef() = 10;

    // Print X
    cout << x;
    return 0;
}

Output:

10

Explanation:
Return type of the above function retByRef() is a reference of the variable x so value 10 will be assigned into the x.