What is Return by Reference in C++

In C++ Programming, not only can you pass values by reference to a function but you can also return a value by reference.

To understand this feature, you should have the knowledge of:

• Global variables

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Example: Return by Reference

#include <iostream>
using namespace std;

// Global variable
int num;

// Function declaration
int& test();

int main()
{
    test() = 5;

    cout << num;

    return 0;
}

int& test()
{
    return num;
}

Output

5

In program above, the return type of function test() is int&. Hence, this function returns a reference of the variable num.

The return statement is return num;. Unlike return by value, this statement doesn't return value of num, instead it returns the variable itself (address).

So, when the variable is returned, it can be assigned a value as done in test() = 5;

This stores 5 to the variable num, which is displayed onto the screen.

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Important Things to Remember When Returning by Reference.

• Ordinary function returns value but this function doesn't. Hence, you cannot return a constant from the function.

  int& test() {
      return 2;
  }

• You cannot return a local variable from this function.

  int& test()
  {
      int n = 2; 
      return n; 
  }