C + + namespace namespace

1 namespaces resolve conflicts of global variables

1 main.h File2 #pragmaOnce3 //the name of the data namespace4 namespaceData5 {6     intnum = -;//External global variable conflict7 }8 9 Ten main.cpp One#include"Main.h" A#include <iostream> - using namespacestd; -  the intnum =Ten; -  - voidMain () - { +cout << Num <<Endl; -cout << data::num << Endl;//:: Domain modifiers must be used here to use the domain action +  ACin.Get(); at}

2 namespaces are not private, all variables, functions are public and can be accessed
Using namespace data;//with namespaces, direct access as global variables
The inner layer covers the outer layers,
:: num accesses global variable directly, global variable does not exist is 0
The use of namespaces must be defined after

#include <iostream>using namespacestd;//namespaces do not have private, all variables, functions are public and can be accessed//using namespace data;//using namespaces, direct access as global variables//the inner layer covers the outer layers,//:: num accesses global variable directly, global variable does not exist is 0//the use of namespaces must be defined afternamespacedata{intnum; voidShow () {cout<< Num <<Endl; }}using namespaceData//using namespaces, direct access as global variables//the inner layer covers the outer layers,namespacedatax{intnum= -; namespaceRun {intnum =Ten; voidShow () {//:: num accesses global variable directly, global variable does not exist is 0cout << Datax::num <<Endl; }    }}using namespacedatax;//the use of namespaces must be defined aftervoidMain () {datax::run::show (); Cin.Get();}voidmain1x () {Data::num=Ten;    Show (); Cin.Get();}

3 Use of namespaces

1#include <iostream>2#include <cstdlib>3 using namespacestd;4 5 6 namespacestring17 {8     Charstr[Ten]{"Calc" };9 }Ten namespacestring2 One { A     Charstr[Ten]{"Notepad" }; - } - //namespace extension, same name, same namespace the //Waterfall-style development - namespacestring2 - { -     Charcmd[Ten]{"Notepad" }; +     voidShow () -     { +cout << str <<Endl; A     } at } -  - //namespaces, which can be nested indefinitely - namespaceRun - { -     namespaceRunit in     { -         namespaceRunitout to         { +             intnum = -; -             voidShow () the             { *cout << Num <<Endl; $             }Panax Notoginseng         } -     } the  + } A  the  + voidMain () - { $     //system (STRING2::STR); $     //string2::show ();//functions and variables for namespaces -Run::runit::runitout::num =199; - run::runit::runitout::show (); the  - Wuyi  theSystem"Pause"); -}

4 Anonymous namespaces

1#include <iostream>2 3 using namespacestd;4 5 6 //Anonymous namespaces equal to global variables7 namespace8 {9     intx =Ten;Ten } One  A  - voidMain () - { thex =3; -cout << x <<Endl; -  -  +Cin.Get(); -  +}

C + + namespace namespace