A namespace is a group of related terms, classes, or attributes that exist within your project. Usually, namespaces have some sort of contextual relevance that influences their structure.

When we start writing any program, we add a pre-processor directive, but it does not end here. Our basics for writing a code include much more than just a pre-processor directive or datatypes. There is a lot more that we might sometimes ignore but are necessary to learn, and one of them is Namespace.

What is Namespace?

A namespace provides scope and order to the identifiers in your code. It is a declarative region that allows us to create logically separate namespaces, thereby preventing name collisions when we include multiple libraries. 

For example, if two libraries declare a class named “vehicle” you can use namespaces to ensure that one version does not override the other when imported into your code.

All identifiers at namespace scope are visible to one another without qualification. Identifiers outside the Namespace can access the members using directive for all the identifiers in the Namespace (using namespace std;).

Example

#include <iostream>    //Example of inclusion directive
using namespace std;
int main(){
std::cout << "Welcome to Geek on Peak" ;
}

Why Using Directive?

A using-directive allows using all the names in a namespace without using the namespace name as an explicit qualifier. If you are using several different identifiers in a namespace; or just using one or two identifiers, then consider the using-declaration only to bring those identifiers into the scope and not all the identifiers in the Namespace.

Example

#include <iostream>
using namespace std;

// first name space
namespace first {
   void func() {
      std::cout << "Inside the first namespace" << endl;
   }
}

// second name space
namespace second {
   void func() {
      std::cout << "Inside the second namespace" << endl;
   }
}

using namespace first;
int main () {
   func();                         // This calls function from first name space.
   return 0;
}

Global Namespace

In C++, they are explicit, meaning that a user or the programmer can create many namespaces in one program. As a result, it cannot be easy to understand code. The namespace operator allows you to explicitly( By the user) declare the current Namespace or separate declarations into different namespaces with little overhead; Instead of declaring them global (implicitly), you just put the namespace scope operator(::) before your symbol.

Std Namespace

All C++ standard library types and functions declared in the std namespace or namespaces nested inside std. The standard library is in the std namespace, which is short for “standard.”

Nested Namespace

As nested means that it is one inside the other, nested namespaces help organize code in large projects and avoid naming collisions with other software projects. An ordinary nested namespace has unqualified access to its parent’s members, but the parent members do not have unqualified access to the nested Namespace (unless inline is declared).

Example

#include <iostream>
using namespace std;

// first name space
namespace first {
   void func() {
      std::cout << "Inside the first namespace" << endl;
   }

// second name space
namespace second {
   void func() {
      std::cout << "Inside the second namespace" << endl;
   }
 }
}
using namespace first::second;
int main () {
   func();     // This calls function from second namespace.//
   return 0;
}

Inline Namespace

In an inline namespace, it treats members as if they were members of the parent namespace. This characteristic enables argument-dependent lookup to work on functions that have overloads in a parent and a nested inline, as well as allows you to declare a specialization in a parent namespace for a template that we declare in the inline.

Syntax

inline namespace ns-name
 { declarations }

FOLLOW-UP

So, You learned about Namespaceand Directives very effectively. If you understood and comprehended this blog properly, well done, you’re getting advanced daily. If, in any case, you’re finding it difficult, you can let us know in the comments & contact us. Besides, if you’ve any doubts, you can post them in the comments. Don’t worry; our geeks will surely get your doubts cleared soon.

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