C++ Namespaces

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In C++ namespaces are used to sort too many classes so that it helps to handle the application.

The global::std refer to the namespace "std".

Defining a Namespace

A namespace definition starts with the keyword namespace.

Syntax:

namespace namespace_name {
   // code declarations
}

Example:

#include <iostream> 
using namespace std;  

namespace first {    
    void welcome() 
    {   
        cout << "Welcome To First Namespace" << endl;          
    }    
}    
namespace second  {    
    void welcome() 
    {   
        cout << "Welcome To Second Namespace" << endl;   
    }    
} 
namespace third  {    
    void welcome() 
    {   
        cout << "Welcome To Third Namespace" << endl;   
    }    
} 
int main()  
{  
    first::welcome(); // Calls function from first namespace.
    second::welcome(); // Calls function from second namespace.
    third::welcome(); // Calls function from third namespace.
    return 0;  
}
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The Using namespace directive

The Using namespace directive helps to avoid prefix of namespaces.

Example:

#include <iostream> 
using namespace std;  

namespace first {    
    void welcome() 
    {   
        cout << "Welcome To First Namespace" << endl;          
    }    
}    
namespace second  {    
    void welcome() 
    {   
        cout << "Welcome To Second Namespace" << endl;   
    }    
} 
namespace third  {    
    void welcome() 
    {   
        cout << "Welcome To Third Namespace" << endl;   
    }    
} 
using namespace third;
int main()  
{  
    welcome(); 
    return 0;  
}
Run ›
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