A reference variable is an alias, that is, another name for an
already existing variable. Once a reference is initialized with a
variable, either the variable name or the reference name may be used to
refer to the variable.
C++ References vs Pointers
References are often confused with pointers but three major differences between references and pointers are:
- You cannot have NULL references. You must always be able to
assume that a reference is connected to a legitimate piece of storage.
- Once a reference is initialized to an object, it cannot be
changed to refer to another object. Pointers can be pointed to another
object at any time.
- A reference must be initialized when it is created. Pointers can be initialized at any time.
Creating References in C++
Think of a variable name as a label attached to the variable's
location in memory. You can then think of a reference as a second label
attached to that memory location. Therefore, you can access the contents
of the variable through either the original variable name or the
reference. For example, suppose we have the following example:
int i = 17;
We can declare reference variables for i as follows.
int& r = i;
Read the & in these declarations as
reference. Thus, read
the first declaration as "r is an integer reference initialized to i"
and read the second declaration as "s is a double reference initialized
to d.". Following example makes use of references on int and double:
#include <iostream>
using namespace std;
int main () {
// declare simple variables
int i;
double d;
// declare reference variables
int& r = i;
double& s = d;
i = 5;
cout << "Value of i : " << i << endl;
cout << "Value of i reference : " << r << endl;
d = 11.7;
cout << "Value of d : " << d << endl;
cout << "Value of d reference : " << s << endl;
return 0;
}
When the above code is compiled together and executed, it produces the following result:
Value of i : 5
Value of i reference : 5
Value of d : 11.7
Value of d reference : 11.7
References are usually used for function argument lists and function
return values. So following are two important subjects related to C++
references which should be clear to a C++ programmer:
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