3. Initializer list order

• Initializer list order should follow the order of data member declarations in your struct or class

• Because constructor call order is very important, modern compilers will generate errors when initializer list does not follow the order of data members. For exaample,

  
  struct Rectangle {
      int width;  // member variable
      int height; // member variable
      char* ptr_name;
  
      Rectangle()
          :
          ptr_name( nullptr ), // out of order
          height( 1 ), // out od order
          width( 1 ) // out of order
      {
          set_name( "UNKNOWN" );
      }
  
      //...
  };//struct Rectangle
  
  

  When compiled with GNU GCC compiler, the above code will give you warning messages like this:

  
   In constructor 'Rectangle::Rectangle()':
  7:11: warning: 'Rectangle::ptr_name' will be initialized after [-Wreorder]
  6:9: warning:   'int Rectangle::height' [-Wreorder]
  9:5: warning:   when initialized here [-Wreorder]
  6:9: warning: 'Rectangle::height' will be initialized after [-Wreorder]
  5:9: warning:   'int Rectangle::width' [-Wreorder]
  9:5: warning:   when initialized here [-Wreorder]