1.1.7 Namespace

• You can use :: to specify global variable name or function if you have same name in you local scope. Or use Base:: to specify Base scope name if you have same name in derived class.
• Usually, namespace should be your project name, you can add company name in front of it if you like.
• There are three kinds of name space usages.
  1. using sp::name;   //then use name, using declaration 
  2. using namespace sp;   //using directive 
  3. sp::name   //specific refer it 
   
  Namespace ns{ 
  Int zy; 
  } 
  using namespace ns; 
  Int main(){ 
  Int zy = 0; //it will hide ns::zy 
  Cin>>zy; //read into local zy 
  }
• Don’t use using directive in any .h file, because It will pollute all the .cpp file which include this head file. Less use it in any .cpp file, you should using scope-resolution more.
• If you have to use using directory, put it after all the include files.
• Do not put more in global-scope, Learn to using namespace instead of global.
• unnamed namespace just like static to specify it to local file scope. At the same time, make anonymous namespace as small as possible. see C++ primer p492
  // a.cpp file 
  static int count; 
   
  // A better method to use namesapce. 
  namespace{ 
  int count; 
  }