Structures

• This material starts on page 478 of the book. READ IT
• A record is a structured data type with a fixed number of components accessed by name. The components may be heterogeneous.
• The individual components of a record are called a field.
• Think of your drivers license.
  • 
  • String data (name, address)
  • Numeric data: height, weight, age
  • Other data (picture, date, ...)
  • These form a record.
• How is a record different from an array? How are they the same?
  • Both can hold multiple data items
  • Array access by index, record by field name
  • Array must be homogeneous, record can be heterogeneous
• In c/c++ a record is implemented as a structure or struct
  • We will look at c style structs
  • C++ style structs are best left alone, use classes instead
• Syntax

  • struct identifier {
        MemberLIst
    };
    

  • A MemberList is much like a set of variable declarations
    • type identifier[, identifier ...];
  • Note the ; at the end. This is required.
• So for the memory game from last time
  • We want to combine two pieces of data, the AnimalT and the state of the board.

  • struct BoardSpace {
       AnimalT contents;
       StatusT status;
    };
    

• While this looks like a variable declaration
  • It is not.
  • This is a blueprint for a variable, not the variable.
  • You do not initialize values
    • g++ allows this, but it is not the thing to do.
• Declaring instances of a struct

   BoardSpace aSquare;
  
   aSquare.contents = RandomAnimalT();
   sSquare.status = StatusT::HIDDEN
  

• Notice we use a . or a member selector to access fields of the structure.
• Domain of a struct
  • Structs can hold any data type, including
    • Arrays
    • Structs.
• Operations on a struct
  • Structs may be passed as all types of parameters (value and reference)
  • Structs may be the return value of a function.
  • Structs may be copied
  • Direct comparison of structs is not implemented.
  • Math on structs is not implemented.
  • Direct I/O of structs is not implemented.
• Add these to the comparison with an array.
• There is much more, but we should get started with some code.