Structured Data Types and Structures

• 10.3 is a one page definition
  • A structured data type is a data type in which each value is a collection of components whose organization is characterized by the method used to access individual components.
  • Never mind.
  • It is just a collection of other data types.
• We will study three of these
  • structures or struct - associated data with no actions.
  • array - a homogeneous collection of data.
  • class - a collection of data an functions.
• We will not study unions
  • They have a place.
  • But they are dangerous, error prone and no longer solve the main problem for which they were created.
• 10.4 discusses records
• A record is a structured data type which a fixed number of components that are accessed by name. The components may be heterogeneous.
  • Important parts: names
  • Heterogeneous.
• Individual components are called fields.
  • Fields are accessed with the member selector operator.
• Records are implemented as a struct in c++.
• I would like to extend my game (remember where creatures meet each other and make friends).
  • I would like each creature to:
    • Keep track of how many other creatures it encounters.
    • Keep track of how many friends it has.
    • Keep track of its size.
• To do this right now I would need to keep three separate variables for each creature.
  • This is bad because it is hard to keep track of.
  • A structure is a better way.
• Syntax

  • struct identifier {
        Memberlist
    }; 

  • Where Memberlist is

  • type identifier[=value|{value}][, identifier];
            

  • Note any valid type may be used.
    • Including user declared types.
    • And structured types.
• I would place this
  • after using namespace std; if I put it in my manin.
  • In a header file if it were part of a "library"
• An example

  • struct PlayerT {
        int age;
        float weight;
        string name;
    };
            

• Declaration and initialization.
  • A variable of this type is declared as normal.
  • And can be initialized with an initializer list.

  • int main() {
        PlayerT player1,
                player2{3,20.0,"Bob"}; 

• Access to member values (or fields)
  • The member selector operator is a .
  • varname.fieldname
  • This can be used on the left or on the right hand side of an equation.

  • player1.name = "Fred";
    player1.age = player2.age;
            

• Operations
  • Records can be
    • Passed as value and reference parameters.
    • Used as a return value from a function.
    • Copied directly under most circumstances.
  • Records can not
    • perform direct input/output

      • cout << player1;   // will not compile
                        

    • Perform direct math.
    • Perform direct comparison.
    • You need to write functions to do this.
• Records can be nested.

  struct NameT {
      string first, middle, last, title;
  };
  
  struct PlayerT {
      NameT name;
      int age;
      float weight;
  };
  
  PlayerT player1;
      player1.name.first = "Bob";