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Re: A good subset of C

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From "Rod Pemberton" <dont_use_email@xnothavet.cqm>
Newsgroups comp.lang.misc
Subject Re: A good subset of C
Date Wed, 07 May 2014 19:04:06 -0400
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On Wed, 07 May 2014 06:55:57 -0400, James Harris  
<james.harris.1@gmail.com> wrote:
> "Rod Pemberton" <dont_use_email@xnothavet.cqm> wrote in message
> news:op.xfesqctt6zenlw@localhost...

>> If you have a preprocessor, you can use it.  If not, I think you'll
>> have to insert an expanded definition everywhere you need it ...,
>> or perhaps implement it within the compiler.  The compiler should
>> have the necessary information to do it since it knows the struct
>> or union layout and sizes of everything in it's symbol tables etc.
>
> Let's take a step back as I didn't clearly explain the point I was making
> about headers. I was thinking that they normally contain the interface
> information for a source file. For a source file called source.c the  
> header will normally be called source.h and it will define all of the
> info that another source file needs in order to interface with functions
> in source.c.
>
> So any program that wants to call services in source.c will #include
> source.h first. That will tell the compiler the interface info it needs
> to know.

That's one way to do it.  That's commonly done for C, but not required.
Personally, I prefer all-in-one programs if they're small.

> What might header source.h contain? Here are two possible types of
> information:
>
> 1. Integer constants. For example, EOF in stdio.h.
> 2. Structs. For example, struct timespec in time.h.
>

function prototypes, structs, unions, enums, #defines, macros, ...

> Header files are a poor mechanism because there is no guarantee that the
> header used when the caller is compiled is the same header that was used
> when the callee is compiled. But with some discipline they can be
> effective.

Should a distinction be maded between a program which includes it's own
header file and a program which includes a C library header file?

In one case, the source which uses those headers are compiled too, but
not for the other.  The other is compiled as a library.

> I was trying to say that things like struct timespec would need to be
> communicated to a program that interfaces with time functions.

So, you're planning to object-orient-ize that struct somehow?  ;-)

> If the caller wants to update field tv_nsec of a struct timespec it
> needs to know its offset and its type at compile time.

Yes.

> Without the header mechanism how could that info be made available
> to the calling module?

Didn't we have some conversation on something like this at least once
before, i.e., in reference to passing structs and data over a network?

It could query what fields the function expects, but I don't quickly
recognize how the code would decide what to put into the fields.

I.e., some intelligence is involved here, which can be captured by the
code, but it's better if each side understands what to expect.  E.g.,
if the calling module expects to pass a struct of a certain format, an
integer, and a string, but the queried function says the struct has
more members, the string is the wrong size, etc how does the callee
fix that?

> What about the EOF example, above? How would a caller which needed
> to know the value of EOF used by the standard IO functions know
> what value EOF had been set to?

That one is more concrete.  If the code was designed to support
different EOF values, then code could query the value the other side
is using and use that.  If the code is compiled for a value
which is different, then the code isn't going to be compatible.

> [better way]

What's with the need for all the abstraction?

Are you still working on object-oriented stuff?


Rod Pemberton

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Thread

A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-05 08:47 +0100
  Re: A good subset of C "BartC" <bc@freeuk.com> - 2014-05-05 10:56 +0100
    Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-05 19:41 +0100
      Re: A good subset of C "BartC" <bc@freeuk.com> - 2014-05-05 21:08 +0100
        Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-05 21:58 +0100
          Re: A good subset of C "BartC" <bc@freeuk.com> - 2014-05-05 22:55 +0100
            Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-06 00:01 +0100
              Re: A good subset of C "BartC" <bc@freeuk.com> - 2014-05-06 00:44 +0100
          Re: A good subset of C "BartC" <bc@freeuk.com> - 2014-05-06 09:45 +0100
  Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-05 07:33 -0400
    Re: A good subset of C "BartC" <bc@freeuk.com> - 2014-05-05 19:14 +0100
    Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-05 20:12 +0100
      Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-05 18:57 -0400
        Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-07 11:55 +0100
          Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-07 19:04 -0400
            Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-08 10:14 +0100
              Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-08 07:35 -0400
                Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-08 16:22 +0100
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-09 16:45 -0400
                Re: A good subset of C "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2014-05-10 09:04 +0200
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-10 16:30 -0400
                Re: A good subset of C "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2014-05-11 11:59 +0200
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-11 11:06 -0400
                Re: A good subset of C Kaz Kylheku <kaz@kylheku.com> - 2014-05-12 00:26 +0000
                Re: A good subset of C "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2014-05-12 09:54 +0200
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-12 20:01 -0400
                Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-14 17:45 +0100
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-14 18:11 -0400
                Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-14 23:54 +0100
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-14 19:43 -0400
                Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-17 18:00 +0100
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-17 16:00 -0400
                Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-17 22:17 +0100
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-17 19:58 -0400
                Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-18 07:59 +0100
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-18 13:10 -0400
                Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-19 00:54 +0100
                Re: A good subset of C Andy Walker <news@cuboid.co.uk> - 2014-05-15 01:31 +0100
                Re: A good subset of C BGB <cr88192@hotmail.com> - 2014-05-14 23:43 -0500
                Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-17 18:38 +0100
                Re: A good subset of C Ian Collins <ian-news@hotmail.com> - 2014-05-25 11:04 +1200
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-24 20:36 -0400
                Re: A good subset of C Ian Collins <ian-news@hotmail.com> - 2014-05-25 12:53 +1200
                Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-24 21:34 -0400
                Re: A good subset of C Ian Collins <ian-news@hotmail.com> - 2014-05-25 14:11 +1200
                Re: A good subset of C Kaz Kylheku <kaz@kylheku.com> - 2014-05-25 06:47 +0000
                Re: A good subset of C Kaz Kylheku <kaz@kylheku.com> - 2014-05-25 06:43 +0000
  Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-05 20:59 +0100
    Re: A good subset of C "BartC" <bc@freeuk.com> - 2014-05-05 22:28 +0100
      Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-05 18:57 -0400
        Re: A good subset of C "BartC" <bc@freeuk.com> - 2014-05-06 00:26 +0100
      Re: A good subset of C George Neuner <gneuner2@comcast.net> - 2014-05-06 14:21 -0400
        Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-07 15:43 +0100
          Re: A good subset of C George Neuner <gneuner2@comcast.net> - 2014-05-07 16:03 -0400
            Re: A good subset of C "BartC" <bc@freeuk.com> - 2014-05-07 21:31 +0100
          Re: A good subset of C BGB <cr88192@hotmail.com> - 2014-05-07 15:41 -0500
    Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-05 18:46 -0400
      Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-06 00:42 +0100
        Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-06 06:48 -0400
          Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-07 15:40 +0100
            Re: A good subset of C "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-08 06:50 -0400
              Re: A good subset of C "James Harris" <james.harris.1@gmail.com> - 2014-05-08 15:43 +0100
                Re: A good subset of C George Neuner <gneuner2@comcast.net> - 2014-05-08 14:41 -0400
  Re: A good subset of C BGB <cr88192@hotmail.com> - 2014-05-05 19:08 -0500

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