We all are familiar with an
alias in
C++. An alias means another name for some entity. So, a reference variable is an alias that is another name for an existing variable/object etc.
Below is the program for adding reference to a variable:
Output:
Value of a: 9
After Update:
Value of a :100
Value of N :100
Explanation: In the above program, a variable
a is an alias of variable
N that means we have given another name to variable
N. So what ever we are doing with
a it will effect
N also and vice-versa.
Therefore, when we change the value of
a to 100, then, value of N also changed to be 100.
:
The above method is correct to give an alias to any variable but in the case of
containers the above method will throw a
Compilation Error because containers directly can't store the references, But there is an alternative way of doing the same. The template
std::reference_wrapper in
C++ STL is used to give reference to any containers in C++. The
std::reference_wrapper is a class template that wraps a reference in a copyable, assignable object. It is frequently used as a mechanism to store references inside standard containers(like in
vector,
list, etc) which cannot normally hold references.
Below is the program for adding a reference of an object in container class:
Output:
Value of a for object obj is 5
After Update
Value of a for object obj is 700
Value stored in the list is 700
Explanation:
In the above program, when an object is created of class gfg, the constructor is called and the value of variable a is initialized to 5. We have stored the reference of the object in the list and then we have changed the value of the variable a to 700 by calling the member function
setValue(). Now, when we see the value of the property a of the object whose reference we had stored in the list. The value stored is 700.
