What is a namespace?(C++)

Answers

•   
  

  Namespaces are regions which are used to provide scope for identifiers (variables, classes, functions, etc). Any identifier declared within a namespace cannot be directly accessed outside that namespace.

  Let’s see an example.

  Suppose we have a namespace named num. We declared a variable named a inside this namespace and assigned it a value 2.

  Syntax to declare the namespace num

  namespace num
  

  Now, to access the variable a outside the namespace num, we have to use the operator :: as shown below.

  num::a
  

  Here is the whole code.

  #include <iostream>
  
  namespace num { 
  	int a = 2;
  }
  
  int main(void) {
  	std::cout << num::a << std::endl;
  	return 0;
  }
  

  We can also use the keyword using to introduce the variable a outside the scope of the namespace num.

  #include <iostream>
  
  namespace num { 
  	int a = 2;
  }
  
  int main(void) {
  	using num::a;
  	std::cout << a << std::endl;
  	return 0;
  }
  

  Alternatively, we can introduce the whole namespace num using the using keyword.

  #include <iostream>
   
  namespace num { 
  	int a = 2;
  }
   
  int main(void) {
  	using namespace num;
  	std::cout << a << std::endl;
  	return 0;
  }
  

  Similarly, cout and endl are defined in the std namespace.

  
  

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