Re: What is the right way to do this simple thing

From	cri@tiac.net (Richard Harter)
Newsgroups	comp.lang.c
Subject	Re: What is the right way to do this simple thing
Date	2012-03-11 17:23 +0000
Message-ID	<4f5cd861.2023333794@text.giganews.com> (permalink)
References	(3 earlier) <9s28jrFf51U2@mid.individual.net> <4f5bf4f9.1965115079@text.giganews.com> <9s2cmhFf52U1@mid.individual.net> <4f5c2af2.1978932789@text.giganews.com> <9s360cFa8vU1@mid.individual.net>

Show all headers | View raw

On Sun, 11 Mar 2012 21:27:56 +1300, Ian Collins <ian-news@hotmail.com>
wrote:

>On 03/11/12 05:46 PM, Richard Harter wrote:
>> On Sun, 11 Mar 2012 14:15:52 +1300, Ian Collins<ian-news@hotmail.com>
>> wrote:
>>
>>> On 03/11/12 01:44 PM, Richard Harter wrote:
>>>> On Sun, 11 Mar 2012 13:06:18 +1300, Ian Collins<ian-news@hotmail.com>
>>>> wrote:
>>>>>
>>>>> Why don't you just use the usual union in a struct technique?
>>>>
>>>> You might spell out what you think "the usual"  is; I looked at
>>>> several variations and it looked like there were subtle problems with
>>>> all of them.  Perhaps I missed something.
>>>
>>> struct load_package {
>>>    message_type type;       /* The type has access info    */
>>>    size_t       total_len;  /* Total length of the package */
>>>    size_t       data_len;   /* Length of the data          */
>>>    union {
>>>      payload_type1;
>>>      payload_type2;
>>>    } payload;
>>> };
>>
>> Unless you have something in mind that I'm missing this won't do at
>> all.  First of all there is no guarantee of alignment - there may have
>> to be padding between data_len and the union.
>
>So?  Using a union solves the alignment issue - it will be correctly 
>aligned.

Ah, I assumed that if you were using my notation you were following my
coding sequence.  In my posting "struct load_package" was an
auxilliary structure used to construct the deliverable "struct
package".  You were using your "struct load_package" as the
deliverable.  So yes, if that is your deliverable it will be correctly
aligned.

>
>> Secondly I really hope
>> you aren't suggesting that every different payload type in a program
>> must be in that union.
>
>Well that depends on the relationship between the types.  If they are 
>related, why not?  The X11 Event structure has a couple of dozen or so 
>structs in its union member.

Assume that the number of types may be in the hundreds.  Assume that
with each new applications new message types may be added.  Assume
that the different payloads aren't necessarily related.  Assume that
maintenance nightmares are unwanted.

I really do want the package structures to be simple!

>> The point of the second bit of code that I did is that it does take
>> care of alignment and doesn't drag in stuff from all other
>> serializations.
>
>?

Did you read that code?  It's pretty simple.  The key is that
different packages can have different offsets for the deliverable
data; all that is really required is that the payload is correctly
aligned and that the package specifies where it starts.

The issue with it is where the code for doing the load lives.

Thank you for the comments.

Thread

What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-10 19:26 +0000
  Re: What is the right way to do this simple thing Don Y <this@isnotme.com> - 2012-03-10 12:57 -0700
  Re: What is the right way to do this simple thing ImpalerCore <jadill33@gmail.com> - 2012-03-10 14:12 -0800
    Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-10 23:31 +0000
      Re: What is the right way to do this simple thing Ian Collins <ian-news@hotmail.com> - 2012-03-11 13:06 +1300
        Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 00:44 +0000
          Re: What is the right way to do this simple thing Ian Collins <ian-news@hotmail.com> - 2012-03-11 14:15 +1300
            Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 04:46 +0000
              Re: What is the right way to do this simple thing Ian Collins <ian-news@hotmail.com> - 2012-03-11 21:27 +1300
                Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 17:23 +0000
                Re: What is the right way to do this simple thing Ian Collins <ian-news@hotmail.com> - 2012-03-12 10:01 +1300
                Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-13 21:18 +0000
                Re: What is the right way to do this simple thing Ian Collins <ian-news@hotmail.com> - 2012-03-14 10:23 +1300
              Re: What is the right way to do this simple thing Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-03-11 11:59 +0000
                Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 16:51 +0000
                Re: What is the right way to do this simple thing Gene <gene.ressler@gmail.com> - 2012-03-13 07:32 -0700
                Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-13 21:46 +0000
      Re: What is the right way to do this simple thing ImpalerCore <jadill33@gmail.com> - 2012-03-12 07:28 -0700
        Re: What is the right way to do this simple thing ImpalerCore <jadill33@gmail.com> - 2012-03-12 08:13 -0700
        Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-13 21:51 +0000
  Re: What is the right way to do this simple thing Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-10 14:21 -0800
    Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 01:40 +0000
      Re: What is the right way to do this simple thing Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-11 14:11 -0700
        Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-13 21:56 +0000
          Re: What is the right way to do this simple thing Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-14 14:55 -0700
            Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-15 21:55 +0000
              Re: What is the right way to do this simple thing Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-19 13:33 -0700
  Re: What is the right way to do this simple thing Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-03-10 15:21 -0800
    Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 00:47 +0000
  Re: What is the right way to do this simple thing Philip Lantz <prl@canterey.us> - 2012-03-11 01:07 -0800
    Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 16:14 +0000
  Re: What is the right way to do this simple thing Markus Wichmann <nullplan@gmx.net> - 2012-03-11 13:47 +0100
    Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 16:24 +0000
  Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 21:01 +0000
    Re: What is the right way to do this simple thing Anders Wegge Keller <wegge@wegge.dk> - 2012-03-12 00:05 +0100
      Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-13 21:57 +0000
    Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-11 23:06 +0000
      Re: What is the right way to do this simple thing Geoff <geoff@invalid.invalid> - 2012-03-11 17:34 -0700
        Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-13 22:00 +0000
          Re: What is the right way to do this simple thing Geoff <geoff@invalid.invalid> - 2012-03-13 18:12 -0700
            Re: What is the right way to do this simple thing cri@tiac.net (Richard Harter) - 2012-03-14 03:38 +0000
              Re: What is the right way to do this simple thing Geoff <geoff@invalid.invalid> - 2012-03-14 00:49 -0700

csiph-web