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Re: C Macro define contain symbol #

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Roberto Waltman <usenet@rwaltman.com> writes:
> Eric Sosman wrote:
>>     ... if you really think you need "pack(1)".  Usually (not always,
>>but usually) that's the sign of a short-term hack leading to long-
>>term headaches.
>
> Not when you are dealing with communication protocols, mapping
> hardware control registers in embedded systems, etc.
> Without the "pack" pragmas, instead of having a structure that
> directly overlaps the desired memory layout, the packing/unpacking
> would have to be in higher level software.
> This is a much needed functionality, and I am puzzled why it never
> became part of the language standard, instead of a not always
> available compiler extension.
> Even Pascal had packed records.

Yes, but Pascal packed records, as I recall, are merely a hint to the
compiler that space should be minimized.  They're not necessarily
suitable for matching a specific externally imposed layout.

One example of a problem that would have to be solved:

    struct foo {
        char c;
        int i;
    };
    #pragma pack(struct foo) /* or whatever the syntax is */

    void some_func(int *p);

    struct foo obj;
    some_func(&obj.i);

I've worked on systems where an int* cannot contain an address that
isn't word-aligned.  Do you forbid taking the address of a member of a
packed struct?

Ada has "pragma Pack", which is a hint to minimize space, *and* an
elaborate system of representation clauses that let you specify layout
down to the bit level.

C has unsigned char[], memcpy(), and bit masks.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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C Macro define contain symbol # Wang WolfLouis <wolflouiswang@gmail.com> - 2011-09-13 02:47 -0700
  Re: C Macro define contain symbol # Noob <root@127.0.0.1> - 2011-09-13 13:14 +0200
  Re: C Macro define contain symbol # Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-13 07:55 -0400
    Re: C Macro define contain symbol # Roberto Waltman <usenet@rwaltman.com> - 2011-09-13 08:24 -0400
      Re: C Macro define contain symbol # Keith Thompson <kst-u@mib.org> - 2011-09-13 11:12 -0700
        Re: C Macro define contain symbol # Keith Thompson <kst-u@mib.org> - 2011-09-13 20:19 -0700
          Re: C Macro define contain symbol # Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-09-16 00:43 +0300
            Re: C Macro define contain symbol # Keith Thompson <kst-u@mib.org> - 2011-09-15 18:34 -0700
        Re: C Macro define contain symbol # Richard Damon <news.x.richarddamon@xoxy.net> - 2011-09-13 22:51 -0400
          Re: C Macro define contain symbol # Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-09-14 12:16 +0100
      Re: C Macro define contain symbol # tom st denis <tom@iahu.ca> - 2011-09-13 11:20 -0700
      Re: C Macro define contain symbol # Ian Collins <ian-news@hotmail.com> - 2011-09-14 07:55 +1200
      Re: C Macro define contain symbol # Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-14 07:58 -0400
        Re: C Macro define contain symbol # Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-09-14 14:54 +0000
      Re: C Macro define contain symbol # Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-09-16 00:34 +0300
        Re: C Macro define contain symbol # Nobody <nobody@nowhere.com> - 2011-09-16 12:07 +0100
    Re: C Macro define contain symbol # "BartC" <bc@freeuk.com> - 2011-09-13 13:50 +0100
      Re: C Macro define contain symbol # James Kuyper <jameskuyper@verizon.net> - 2011-09-13 08:59 -0400
        Re: C Macro define contain symbol # Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-09-14 15:02 +0000
  Re: C Macro define contain symbol # Kenneth Brody <kenbrody@spamcop.net> - 2011-09-13 16:54 -0400

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