What is a Pass by Reference?

When a variable is passed as a reference to a function, the address of the variable is stored in a pointer variable inside the function. Hence, the variable inside the function is an alias for the passed variable. Therefore, any operations performed on the variable inside the function will also be reflected in the calling function. 

• This ability to reflect changes could return more than one value by a function. 
• Also, a void function could technically return value/s using this method. 

The & (address of) operator denotes values passed by pass-by-reference in a function. Below is the C++ program to implement pass-by-reference:

Explanation:

• Firstly a function is defined with the return datatype void and takes in value by reference (as denoted by the & address sign in the formal parameters). 
• The function decrements the value of its formal parameter by 1. 
• After which, inside the main function, an integer variable named a is initialized with the value 5. 
• The value of ‘a’ is printed on the console. The f() function is called, and the variable is passed as an argument. 
• Inside the function, the variable’s value is decremented by 1.
• Upon returning from the function, the variable’s value is again displayed, which turned out to be 1 less than the original value. 

Hence, the changes to a variable passed by reference to a function are reflected in the calling function.

Several ways exist in which data (or variables) could be sent as an argument to a function. Two of the common ones are Passing by Value and Passing by Reference. Passing by reference allows a function to modify a variable without creating a copy. We have to declare reference variables. The memory location of the passed variable and parameter is the same. Therefore, any change to the parameter also reflects in the variable inside its parent function. This article focuses on discussing how to pass variables by reference in C++.