Building Your own data types

• typedef existingname new name
  • typedef int NumberType;
  • This is useful when you want to think about data in a different way.
    • You may want to allow for future changes in your code.
      • Develop your code with typedef float real;
      • later replace this with typedef long double real;
      • This is sort of equivalent to declaring a constant.
    • You may want to think about something differently and the label will make this easier. More on this later.
    • You may want to declare your own data type, with a reasonable name, but more on this later.
• Enumerated Types
  • You can declare your own type with it's own values it can assume.
  • This is an simple type.
  • enum typename { enumerator1, enumator2, ... enumatorn}
  • enum typename { enumerator1=intConstat, enumator2=intConstant, ... enumatorn=intConstant}
  • enum MonthT {JANUARY, FEBRUARY, MARCH, APRIL, MAY, JUNE, JULY, AUGUST, SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER};
  • This declares a new type, MonthT, which we can
    • Declare constants and variables,
    • Declare routines which take/return values of this type
    • Declare more complex types constructed from this type (eventually)
  • The rules
    • The type must be a valid identifier
    • I think UpperCaseT would be good for identifiers
    • The enumerators (values inside of {}) are also identifiers
    • They should be treated as constants when naming.
  • You can increment enumerated type variables
    • They are mapped to the integers, so it works
    • But what happens is the type is coerced to an int and the result is an int.
    • So it must be cast back to the enumerated type
    • MonthT m=JANUARY;
    • MonthT(m+1)
• Generally when you build a new type, you build a set of supporting routines to accompany it.
• You also build any constants necessary to support them.
• When building an enumerated type I almost always
  • Build a routine that takes a version of the enumerated type and returns a corresponding string.
  • Build a routine that takes a string and returns the corresponding type
  • Build FIRST_ and LAST_ constants
  • Build _SIZE
• Please see myCal.C