[c++] namespace namespace

[c++] namespace

        1. Definition of namespace

        2. Using command

        3. The relationship between classes and namespaces

 

refer to:

"C++ from entry to proficient" People's Posts and Telecommunications Publishing House

 

1. Definition of namespace

        Namespace is the namespace. A file is a physical way of dividing a program into chunks, while a namespace is a logical way of dividing a program into chunks.

        C++ uses a single global variable namespace. In this single space, if there are two variables or functions with the same name, a conflict will occur. Namespace is a mechanism introduced to solve the naming conflict of variables and functions in C++. The main idea is to define variables in namespaces with different names.

        For example, there are Class 1 of Senior 1 in No. 1, and Class 1 of Senior 1 in No. 2, but because they belong to different schools, we can correctly distinguish these two classes.

Benefits of namespaces:

1. Avoid naming conflicts

2. Simplify access to class members

 

Programming example: call the print() function in two different namespaces respectively

//namespace.cpp

#include<iostream>
using namespace std;

namespace name_1 //namespace 1
{
	void print()
	{
		cout<<"Call print() in name_1 space"<<endl;
	}
}

namespace name_2 //namespace 1
{
	void print()
	{
		cout<<"Call print() in name_2 space"<<endl;
	}
}


intmain()
{
	name_1::print(); //Call print() in the name_1 space, "::" is the scope resolution operator
	name_2::print(); //call print() in name_2 space
	
	return 0;
}

operation result:

            

Analysis: Use the scope resolution operator "::" to call the function print() in the namespace.

 

Name of the namespace:

        To simplify names, namespaces can be aliased with abbreviations, etc.

        Namespace IBM=International_Business_Machine_Corporation

        Then you can IBM::print();

 

2. using directive

For example the most commonly used: using namespace std;

Note : The scope of the using directive . usingnamespace is only valid within the statement block in which it is declared (a statement block refers to a group of instructions within a pair of curly braces {}).

intmain()
{
	{ //block 1
		using namespace name_1;
		name_1::print(); //call print() in name_1 space
	}
	
	{ //block 2
		using namespace name_2;
		name_2::print(); //call print() in name_2 space
	}
	
	return 0;
}

operation result:

            

 

3.  The relationship between classes and namespaces

    Namespaces are a way of organizing classes. If a class is compared to a file in a computer, a namespace is like a folder, which implements the classification management of classes, and adds structure and hierarchical organization to the class library.

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