What is a reference variable in C++?

A reference variable in C++ serves as an alias for another variable, allowing you to manipulate the value of the original variable without needing to use a pointer or explicitly address its memory location. When you declare a reference variable, it does not get its own separate memory space; instead, it refers directly to the memory location of the variable it is linked to. This means that any changes made to the reference variable reflect in the original variable, providing a convenient way to work with variable data.

This concept is particularly useful in function parameter passing, where references can be used to avoid the overhead of copying large amounts of data while still allowing the function to modify the original data. In contrast to other options, a reference is not a pointer, does not refer to library functions, and is not an immutable variable.