Re: Porting Experiences (was Ada and Pascal etc )

["Marin David Condic, 561.796.8997, M/S 731-96" <condicma@PWFL.COM>]

Lawrence Kirby <fred@GENESIS.DEMON.CO.UK> writes:
>The portability implications of this are small or non-existent (there may
>be performace implications in rare circumstances, and issues relating to
>data sizes and external data formats). As ever the C language is designed
>with the assumption that the programmer knows what he is doing. The use
>of ranges implies that you know beforehand what those ranges will be.
>In C you follow a set of rules:
>
    I think you missed a very important point and one that has trashed
    many attempted ports in my experience.

    While the rules you cite do guarantee a minimum accuracy and
    intelligent use thereof certainly does help things, what do you do
    about all the representation issues? Technically, that integer you
    specify as needing a minimum of 16 bits could get represented with
    32 bits. Suppose that it is used in an I/O record to a data file?
    Now you're incompatible with all the data files built by another
    version which allocated only 16 bits. Or suppose it is passed as a
    parameter to an OS routine or routine written in another language
    or a routine written in C but compiled with a different compiler?

    There are *many* occasions where the internal representation of a
    data item is *critical* to the success of a system. Hence not
    having the ability to explicitly state what sort of representation
    is required can hurt portability. I don't see why C can't be
    modified in some subsequent standard to let the programmer dictate
    that a given number be represented a certain way, so I don't think
    it is the end of the world. But as things stand now, this is a
    weakness in the language that hurts portability and if something
    *does* successfully port without changes, it happens more by
    accident than by design.

    MDC

Marin David Condic, Senior Computer Engineer     Voice:     561.796.8997
Pratt & Whitney GESP, M/S 731-96, P.O.B. 109600  Fax:       561.796.4669
West Palm Beach, FL, 33410-9600                  Internet:  CONDICMA@PWFL.COM
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