C++ Namespaces

Namespaces in C++ are used to organize too many classes so that it can be easy to handle the application.

For accessing the class of a namespace, we need to use namespacename::classname. We can use using keyword so that we don’t have to use complete name all the time.

In C++, global namespace is the root namespace. The global::std will always refer to the namespace “std” of C++ Framework.


C++ namespace Example

Let’s see the simple example of namespace which include variable and functions.

 
  • #include <iostream>  
  • using namespace std;  
  • namespace First {    
  •     void sayHello() {   
  •         cout<<“Hello First Namespace”<<endl;          
  •     }    
  • }    
  • namespace Second  {    
  •        void sayHello() {   
  •            cout<<“Hello Second Namespace”<<endl;   
  •        }    
  • }   
  • int main()  
  • {  
  •  First::sayHello();  
  •  Second::sayHello();  
  • return 0;  
  • }  

Output:

Hello First Namespace
Hello Second Namespace

 

C++ namespace example: by using keyword

Let’s see another example of namespace where we are using “using” keyword so that we don’t have to use complete name for accessing a namespace program.

 
  • #include <iostream>  
  • using namespace std;  
  • namespace First{  
  •    void sayHello(){  
  •       cout << “Hello First Namespace” << endl;  
  •    }  
  • }  
  • namespace Second{  
  •    void sayHello(){  
  •       cout << “Hello Second Namespace” << endl;  
  •    }  
  • }  
  • using namespace First;  
  • int main () {  
  •    sayHello();  
  •    return 0;  
  • }  

Output:

Hello First Namespace