Namespaces in C++

February 14, 2023

C++ Namespaces

In C++, a namespace is a container for identifiers (i.e. names of types, functions, variables, etc.). It is used to organize code and prevent naming conflicts. Namespaces are defined using the namespace keyword, and an identifier is added to a namespace using the scope resolution operator (::). Let us learn everything about namespaces in C++ over here.

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Namespaces in C++

To access an identifier in a namespace, you use the scope resolution operator. For example, to call the print_x function in the my_namespace namespace, you would use my_namespace::print_x();

You can also use using namespace directive to make all the identifiers in a namespace available without the need to qualify them with the namespace name.

using namespace my_namespace;
print_x();

For example:

Run

namespace my_namespace {
    int x = 5;
    void print_x() {
        cout << x << endl;
    }
}

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Namespace in C++

Run

// A C++ program to demonstrate use of class
// in a namespace
#include <iostream>
using namespace std;

namespace ns
{
	// A Class in a namespace
	class prepster
	{
	public:
		void display()
		{
			cout<<"ns::prepster::display()"<<endl;;
		}
	};
}

int main()
{
	// Creating Object of prepster Class
	ns::prepster obj;

	obj.display();

	return 0;
}

Output

ns::prepster::display()

There are several ways to use a namespace in C++:

  1. Using the scope resolution operator (::) to access identifiers within a namespace. For example, if you have a variable x in a namespace my_namespace, you can access it by using my_namespace::x.

  2. Using the using directive to bring all identifiers from a namespace into the current scope. For example, if you want to use all identifiers in the my_namespace namespace, you can use using namespace my_namespace;.

  3. Using the using declaration to bring a specific identifier from a namespace into the current scope. For example, if you want to use only the x variable in the my_namespace namespace, you can use using my_namespace::x;.

It’s important to note that it’s a best practice to be explicit about what symbols you’re importing and where they come from, instead of using using namespace in header files, as it can lead to naming conflicts and make code harder to understand.

It’s also important to note that, when you use using directive it will make all the identifiers in a namespace available without the need to qualify them with the namespace name, and if you have same identifier in different namespace, it will lead to naming conflict.

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