Constructors and Construction

• Constructors are necessary to initialize private member data.
• Threre are three ways to do this.
  • in-class member initializers
    • Like initializing a variable, this is done in the class definition

    • class SomeClassT {
      ...
         private:
            int avar{4};
            ...  

  • member initializer lists
    • This is done in a "pre constructor" area.
    • Any object members of a class are constructed before the construtor code is executed.
    • Some items must be initialized at construction.
      • Reference member variables for example.
    • To do this, we can use code such as

    • class FooT {
        public:
             FooT(typeA paramA):
                 var1{initialValue}, var2{initialvalue} ... 
                 {
                 }
        private:
             type1 var1;
             type2 var2;
             ...  }
                  

    • This code will run as the objects (var1, var2, ...) are constructed
    • Note that the objects are constructed in the order they are declared in the definition
    • They must be listed in this order it the member-initializer list.
      • Otherwise errors could occur.
    • Note, later we will discuss parent class construction, which occurs before this.
  • Finally objects may be changed in the constructor body.
• See initial.cpp
• This is important for reference member data
• See game.cpp
• Exceptions and ctor initializers

  • constructor () 
    try 
        : initilizer 
    {
        // normal constructor body
    } catch {
        // free raw pointers or other raw resources.
        //    remember the destructor will not be called.
        // log errors
    
        // throw a new exception
    }
            

  • In the catch
    • Paramters are available.
    • But constructed member objects are not!
    • You must throw another exception, or the runtime system will do it for you.
• In destructors, throws cause the program to terminate