Programming Tutorials

What Is a Reference in C++?

By: Manoj Kumar in C++ Tutorials on 2007-09-14  

A reference is an alias; when you create a reference, you initialize it with the name of another object, the target. From that moment on, the reference acts as an alternative name for the target, and anything you do to the reference is really done to the target.

You create a reference by writing the type of the target object, followed by the reference operator (&), followed by the name of the reference. References can use any legal variable name, but for this book we'll prefix all reference names with "r." Thus, if you have an integer variable named someInt, you can make a reference to that variable by writing the following:

int &rSomeRef = someInt;

This is read as "rSomeRef is a reference to an integer that is initialized to refer to someInt." Program below shows how references are created and used.


NOTE: Note that the reference operator (&) is the same symbol as the one used for the address of the operator. These are not the same operators, however, though clearly they are related.

Creating and using references.

1:    //
2:    // Demonstrating the use of References
4:    #include <iostream.h>
6:    int main()
7:    {
8:         int  intOne;
9:         int &rSomeRef = intOne;
11:        intOne = 5;
12:        cout << "intOne: " << intOne << endl;
13:        cout << "rSomeRef: " << rSomeRef << endl;
15:        rSomeRef = 7;
16:        cout << "intOne: " << intOne << endl;
17:        cout << "rSomeRef: " << rSomeRef << endl;
18:   return 0;
19: }

Output: intOne: 5
rSomeRef: 5
intOne: 7
rSomeRef: 7

Anaylsis: On line 8, a local int variable, intOne, is declared. On line 9, a reference to an int, rSomeRef, is declared and initialized to refer to intOne. If you declare a reference, but don't initialize it, you will get a compile-time error. References must be initialized.
On line 11, intOne is assigned the value 5. On lines 12 and 13, the values in intOne and rSomeRef are printed, and are, of course, the same.

On line 15, 7 is assigned to rSomeRef. Since this is a reference, it is an alias for intOne, and thus the 7 is really assigned to intOne, as is shown by the printouts on lines 16 and 17.

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