NetNews Usenet Archive 1992 #26/NN_1992_26.iso/spool/comp/lang/cplus/16109

Internet Message Format | 1992-11-11 | 2.6 KB

Xref: sparky comp.lang.c++:16109 comp.std.c++:1538
Newsgroups: comp.lang.c++,comp.std.c++
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From: [e-mail] (John MAX Skaller)
Subject: Re: PROPOSAL: Hidden private parts of classes
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Organization: MAXTAL P/L C/- University Computing Centre, Sydney
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Date: Wed, 11 Nov 1992 18:15:20 GMT
Lines: 47

In article <[e-mail]> [e-mail] (Klamer Schutte) writes:
>In <[e-mail]> [e-mail] (John MAX Skaller) writes:
>
>]In article <[e-mail]> [e-mail] (Klamer Schutte) writes:
>
>]>OK, that holds for global / static variables. But how for auto variables?
>]>These generally are efficient to use, but to be efficient, their size
>]>must be known at compile time.
>
>]    Why? Why cant the size be calculated by a smart linker
>]at link time? Why cant assembly output be made by the compiler
>]with 'sizeof_someobject' as a symbol yet to be determined?
>
>]>and thus can only a pointer to an object on the heap be used.
>
>]    NO, and I have SEEN it done otherwise in a Modula compiler,
>]I used it and it worked.
>
>I doubt it. I can't see how a compiler can build a stack frame with
>auto variables, if the sizes of the elements on the stack frame are
>unknown.

    The Modula compiler looks up the last definition of the type
and uses the size of that. If subsequently the system finds that
its been changed, auto-dependency checking causes the module
to be re-compiled.

    As I said before this requires environment support to
work, and is unlikely to be workable for C++ which doesnt have
the ability to pre-compile a class interface declaration.
Modula has separate INTERFACE and IMPLEMENTATION sections
for modules and it is possible to do this. Modula *requires*
environment support because it has a USE MODULENAME statment,
whereas C has #include filename. Modula has to associate
the internal MODULENAME with an external file containing
the precompiled module interface anyhow.

    So thats how it works. It was done deliberately to
avoid using a pointer on the stack.



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        JOHN (MAX) SKALLER,         [e-mail]
    Maxtal Pty Ltd, 6 MacKay St ASHFIELD, NSW 2131, AUSTRALIA
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