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Groups > comp.lang.misc > #2209

Re: A good subset of C

From "James Harris" <james.harris.1@gmail.com>
Newsgroups comp.lang.misc
Subject Re: A good subset of C
Date 2014-05-07 11:55 +0100
Organization A noiseless patient Spider
Message-ID <lkd3fo$2mv$1@dont-email.me> (permalink)
References <lk7flm$m95$1@dont-email.me> <op.xfdw11vx6zenlw@localhost> <lk8nrc$ov4$1@dont-email.me> <op.xfesqctt6zenlw@localhost>

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"Rod Pemberton" <dont_use_email@xnothavet.cqm> wrote in message 
news:op.xfesqctt6zenlw@localhost...
> On Mon, 05 May 2014 15:12:47 -0400, James Harris 
> <james.harris.1@gmail.com> wrote:
>> "Rod Pemberton" <dont_use_email@xnothavet.cqm> wrote in message 
>> news:op.xfdw11vx6zenlw@localhost...
>
>> But I cannot think how to bring in the definitions of structs
>> (from which field offsets are calculated) without header files.
>
> Well, I mentioned these:
> address of - address operator & - part of C
> sizeof() operator - part of C
> typeof - part of the compilers
> alignof - part of the compiler
>
> But, I forgot this one:
> offsetof() - part of C (macro in stddef.h)
>
> offsetof() gets the offsets of something, like the element of a struct
> or union.  Look at the macro in stddef.h or Google "offsetof macro".

Thanks, I didn't know about offsetof.

...

> 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.

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.

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.

I was trying to say that things like struct timespec would need to be 
communicated to a program that interfaces with time functions. 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. Without the header mechanism how could 
that info be made available to the calling module?

>> Could #if and friends be omitted, for example by including
>> executable tests in the code?
>
> #if #endif #ifdef could be replaced by regular if statements,
> with a flag or variable to indicate which code is active.

Good.

> #define's in the code can be replaced with the value or expanded
> macro, etc.

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?

> I don't think there is an easy way to handle #include, except
> cut-n-paste the entire include ...

Not sure. Maybe the individual parts which are #included could be 
communicated in some other - better - way.

James

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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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