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:
Example: Return by Reference
#include <iostream>
using namespace std;
// global variable
int num;
// function declaration
int& test();
int main() {
// assign 5 to num variable
// equivalent to num = 5;
test() = 5;
cout << num;
return 0;
}
// function definition
// returns the num variable by reference
int& test() {
return num;
}
Output
5
In the 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 reference to the variable itself.
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.
Important Things to Remember When Returning by Reference
- We can't return literals from the function that should return lvalue references, since literals can't have lvalue references.
int& test() {
// incorrect
return 2; //returns literal
}
- The object being returned by the function should exist even after the function returns. The local variables are destroyed once the function returns, so we should not return a local variable from the function.
// can't do
int& test() {
int n = 2;
return n; // returns local variable
}
// can do
int& test() {
static int n = 2;
return n; // return static variable by reference
}
Also Read: