Re: Cross-platform issues

[tmoran@acm.org]

> closely as possible to the one that inspired it.  The original
> emits trace data with things like field length info in 4-byte
> integers, for example. I suppose that using a derived type to
> ensure that in my implementation those fields conform with the
> original is one way to do it, but is that accepted practice, or
> is there a more usual one?
  Representation clauses and pragmas let you specify machine
characteristics, for instance that a particular field is 4 bytes long.
Types, and derived types, generally have to do with the logical nature of
the data
eg
type Field_Lengths is range 1 .. 64;
type Water_Temperatures is range 32 .. 212;
type Car_Mileages is range 0 .. 400_000;
etc
An item of any of those types would fit in a four byte field, even
though the first two types could fit in a single byte.  In the absence
of a representation clause, the compiler is allowed to choose whatever
it likes.  If you want something *represented* the same on two different
machines, or via two different compilers, use representation clauses.