Structures

• Read 10.4 Records (structs) starting on page 478
• Structures or structs are old, part of c
• Stroustrup modified them somewhat, but we will be using the c style
  • C++ allows us to declare access permission to fields.
  • And to add methods.
  • But common usage does not do this.
  • If you need these constructs you should be using classes.
• Structs allow us to group data
  • Think student id or drivers license.
  • Mutliple fields each of possibly different data types.
  • The fields have different meaning and names.
  • Not a collection of mail boxes.
• Syntax
  • A member_list is

  • datatype identifier;
    datatype identifier, identifier ;
            

  • A struct

  • struct identifier {
        MemberList;
        MemberList;
    };
            

• Example
  • In our game, I want a player to have the following attributes
    • A name of type string.
    • A sanity count of type size_t.
    • A status of type StatusT
  • I would declare the following

    struct PlayerT {
        string name;
        size_t sanity;
        StatusT status;
    };
             

• This is a just a plan for allocating memory, no actual memory is allocated.
• To access the individual fields, you use the member selector ( a dot .)
  • On either the left hand side or right hand side of an equation.

  • PlayerT player1;
    
    player1.name = "Dan";
    player1.sanity = 3;
    player1.status = StatusT::ALIVE;
    
    cout << "The player's name is " << player1.name;
    if (player1.sanity > 0) {
     ...
    }
             

  • Structures are most likely set up in adjacient memory
    • 
  • On page 481 she gives a chart of what you can and can not do with structs.
    • You can
      • pass by value and reference.
      • Return from a function
      • Assign
    • You can not
      • Do direct i/o
      • Do math or comparison
• In modern c++ the most common use of structs is to bind information.
  • We will learn classes soon which are the tool for building objects.
• Write the following
  • ReadPlayer, that reads in the values and returns a PlayerT
  • PrintPlayer, that takes a PlayerT and prints the values.
  • Battle that takes two PlayerT's and does a basic battle.