Next: , Up: Type Definition Possibilities



6.2.11.1 Subrange Types

GNU Pascal supports Standard Pascal's subrange types:

     program SubrangeDemo;
     type
       MonthInt = 1 .. 12;
       Capital = 'A' .. 'Z';
       ControlChar = ^A .. ^Z;  { `^A' = `Chr (1)' is a BP extension }
     begin
     end.

Also possible: Subranges of enumerated types:

     program EnumSubrangeDemo;
     type
       { This is an enumerated type. }
       Days = (Mon, Tue, Wed, Thu, Fri, Sat, Sun);
     
       { This is a subrange of `Days'. }
       Working = Mon .. Fri;
     
     begin
     end.

To increase performance, variables of such a type are aligned in a way which makes them fastest to access by the CPU. As a result, 1 .. 12 occupies 4 bytes of storage on an IA32 CPU.

For the case you want to save storage at the expense of speed, GPC provides a packed variant of these as an extension:

     program PackedSubrangeDemo;
     type
       MonthInt = packed 1 .. 12;
     begin
     end.

A variable of this type occupies the shortest possible (i.e., addressable) space in memory – one byte on an IA32 compatible CPU.

See also: packed.