packed structs

From	JohnF <john@please.see.sig.for.email.com>
Newsgroups	comp.lang.c
Subject	packed structs
Date	2012-09-22 01:54 +0000
Organization	PANIX Public Access Internet and UNIX, NYC
Message-ID	<k3j5or$q37$1@reader1.panix.com> (permalink)

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Any >>portable<< way to accomplish that in c?
Don't want to use __attribute__((__packed__))
or #pragma pack, etc, nor #ifdef's to choose
among whatever alternatives I happen to know
about. It's a requirement that the code remain
portable.

In particular, I'm trying to write blocks that
conform to a binary file format (gif), and can
set up structs for them easily enough, but can't
fwrite(blockstruct,sizeof(blockstruct),1,fileptr),
or the like, due to blockstruct's inevitable
padding (which indeed occurs for gif format blocks).

At the moment, I just have a different func for
each block type that writes out the members of that
particular struct individually... b..o..r..i..n..g.
A generalization of that idea (if portable packing's
not possible) would also be fine: >>if<< there's some
way to reference the members of a struct, passed as
an argument but of unknown (to the func) type, in a
loop, i.e., for(i=0;i<nmembers;i++)thisstruct->member[i].
Then I could offsetof() and sizeof() each member, and
write it out, so just one (much less boring) func
could handle all the different block type structs.

But, afaik, I don't think that thisstruct->member[i]
thing is possible, nor portable packing. So is there
any "one size fits all" way to handle this problem?
I'm sure people must come across it frequently enough
that it's been thought about, and the best possible
approach (among, possibly, several bad alternatives)
has been identified.
-- 
John Forkosh  ( mailto:  j@f.com  where j=john and f=forkosh )

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packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-22 01:54 +0000
  Re: packed structs Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-09-21 23:22 -0400
    Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-22 06:37 +0000
      Re: packed structs "BartC" <bc@freeuk.com> - 2012-09-22 13:47 +0100
        Re: packed structs Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-09-22 14:00 +0100
        Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-22 15:42 +0000
      Re: packed structs Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-09-22 09:13 -0400
      Re: packed structs Johann Klammer <klammerj@NOSPAM.a1.net> - 2012-09-23 03:10 +0200
        Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-23 02:10 +0000
      Re: packed structs Stephen Sprunk <stephen@sprunk.org> - 2012-09-23 11:44 -0500
        Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-23 23:23 +0000
          Re: packed structs Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-09-24 01:59 +0100
            Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-24 02:54 +0000
              Re: packed structs Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-09-24 04:38 +0100
                Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-24 04:07 +0000
                Re: packed structs Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-09-24 12:16 +0100
                Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-24 11:45 +0000
              Re: packed structs "BartC" <bc@freeuk.com> - 2012-09-24 10:18 +0100
                Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-24 11:04 +0000
                Re: packed structs Stephen Sprunk <stephen@sprunk.org> - 2012-09-30 14:21 -0500
                Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-10-01 07:34 +0000
          Re: packed structs Stephen Sprunk <stephen@sprunk.org> - 2012-09-30 13:52 -0500
    Re: packed structs Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-09-22 01:31 -0700
      Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-22 08:53 +0000
        Re: packed structs Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-09-22 14:17 +0000
          Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-22 15:33 +0000
            Re: packed structs Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-09-22 20:43 +0000
            Re: packed structs "BartC" <bc@freeuk.com> - 2012-09-22 22:52 +0100
          Re: packed structs Keith Thompson <kst-u@mib.org> - 2012-09-22 13:47 -0700
            Re: packed structs JohnF <john@forkosh.com.com> - 2012-09-23 00:19 +0000
              Re: packed structs Ian Collins <ian-news@hotmail.com> - 2012-09-23 13:32 +1200
                Re: packed structs JohnF <john@please.see.sig.for.email.com> - 2012-09-23 02:16 +0000
        Re: packed structs Ian Collins <ian-news@hotmail.com> - 2012-09-23 10:33 +1200
          Re: packed structs Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-09-23 01:38 -0700
  Re: packed structs The Great Firewall of China Blue <chine.bleu@yahoo.com> - 2012-09-21 21:29 -0700

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