Re: c prog -plz explain

From	Noob <root@127.0.0.1>
Newsgroups	comp.lang.c
Subject	Re: c prog -plz explain
Date	2014-03-12 15:56 +0100
Organization	A noiseless patient Spider
Message-ID	<lfpsig$4ic$2@dont-email.me> (permalink)
References	(2 earlier) <0.09075131e2de08b336cb.20140310232147GMT.87iorly704.fsf@bsb.me.uk> <fb286c5b-c72d-4615-b613-ac1c27f94107@googlegroups.com> <20140310235955.176@kylheku.com> <lfpa7b$150$1@dont-email.me> <20140312073525.267@kylheku.com>

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Kaz Kylheku wrote:
> On 2014-03-12, Noob <root@127.0.0.1> wrote:
>> Kaz Kylheku wrote:
>>
>>> C is a strongly typed language. It has the concept of type: that an operation
>>> of the correct type must be applied to a datum for well-defined behavior. C has
>>> considerable translation-time type checking in it to support its type system,
>>> but when you use casts, especially for conversions among pointer types, you can
>>> defeat the type system and write programs which break the rules, but do not
>>> produce any diagnostics when compiled, and even make an executable.
>>
>> Ergo, a simple rule for beginners would be: "Don't use casts anywhere".
> 
>> There are very few valid reasons for using casts.

I realize now that I only considered "pointer" casts.

>> One is passing NULL to a variadic function (e.g. execl)
>>
>> Another is trying to define APIs with generic parameters (e.g. connect)
>> i.e. the poor man's polymorphism.
> 
> What if you're calculating  i / j, where i and j are integers, and you
> want an answer like 2.75?
> 
> No i / (double) j for you; stick with two?  :)

Doh!

One trying to abide by the aforementioned "simple rule" could rely
on implicit conversion, as in

  double d_i = i, d_j = j, res = d_i / d_j;

But I do see your point.
Perhaps the rule should be "Don't use pointer casts anywhere"

> The stupid thing is that completely bat-shit unsafe stuff shares the same
> notation with necessary conversions.

Do you have other examples of reasonable use of casts?

Regards.

Thread

c prog -plz explain SAHIL MAHLA <sahilmehla@gmail.com> - 2014-03-10 14:50 -0700
  Re: c prog -plz explain Keith Thompson <kst-u@mib.org> - 2014-03-10 15:41 -0700
    Re: c prog -plz explain Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-10 23:21 +0000
      Re: c prog -plz explain Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-10 23:24 +0000
      Re: c prog -plz explain SAHIL MAHLA <sahilmehla@gmail.com> - 2014-03-10 20:28 -0700
        Re: c prog -plz explain James Kuyper <jameskuyper@verizon.net> - 2014-03-11 00:15 -0400
        Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 07:12 +0000
          Re: c prog -plz explain Noob <root@127.0.0.1> - 2014-03-12 10:43 +0100
            Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 14:38 +0000
              Re: c prog -plz explain Noob <root@127.0.0.1> - 2014-03-12 15:56 +0100
                Re: c prog -plz explain Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-12 11:16 -0400
                Re: c prog -plz explain James Kuyper <jameskuyper@verizon.net> - 2014-03-12 11:36 -0400
                Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 15:38 +0000
              Re: c prog -plz explain glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-12 19:13 +0000
                Re: c prog -plz explain Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-12 16:05 -0400
                Re: c prog -plz explain James Kuyper <jameskuyper@verizon.net> - 2014-03-12 16:32 -0400
                Re: c prog -plz explain Ian Collins <ian-news@hotmail.com> - 2014-03-13 09:38 +1300
                Re: c prog -plz explain Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-29 08:32 -0700
            Re: c prog -plz explain glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-12 19:03 +0000
              Re: c prog -plz explain James Kuyper <jameskuyper@verizon.net> - 2014-03-12 15:33 -0400
                Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 20:56 +0000
                Re: c prog -plz explain Ian Collins <ian-news@hotmail.com> - 2014-03-13 10:07 +1300
        Re: c prog -plz explain "BartC" <bc@freeuk.com> - 2014-03-11 10:33 +0000
  Re: c prog -plz explain Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2014-03-10 18:48 -0400
    Re: c prog -plz explain SAHIL MAHLA <sahilmehla@gmail.com> - 2014-03-10 20:26 -0700
      Re: c prog -plz explain Ian Collins <ian-news@hotmail.com> - 2014-03-11 16:34 +1300
        typecasting (was Re: c prog -plz explain) Jorgen Grahn <grahn+nntp@snipabacken.se> - 2014-03-12 07:03 +0000
          Re: typecasting (was Re: c prog -plz explain) Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 07:40 +0000
            Re: typecasting (was Re: c prog -plz explain) Lowell Gilbert <lgusenet@be-well.ilk.org> - 2014-03-12 10:47 -0400
            Re: typecasting (was Re: c prog -plz explain) Ken Brody <kenbrody@spamcop.net> - 2014-03-12 13:01 -0400
          Re: typecasting (was Re: c prog -plz explain) Richard <rgrdev_@gmail.com> - 2014-03-12 12:47 +0100
            Re: typecasting (was Re: c prog -plz explain) gazelle@shell.xmission.com (Kenny McCormack) - 2014-03-12 12:39 +0000
              Re: typecasting (was Re: c prog -plz explain) Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 15:06 +0000
      Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 07:26 +0000
        Re: c prog -plz explain Richard <rgrdev_@gmail.com> - 2014-03-11 08:39 +0100
          Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 08:08 +0000
      Re: c prog -plz explain Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2014-03-11 09:14 -0400
      Re: c prog -plz explain Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-11 15:38 +0000
  Re: c prog -plz explain Ken Brody <kenbrody@spamcop.net> - 2014-03-11 12:53 -0400
    Re: c prog -plz explain Keith Thompson <kst-u@mib.org> - 2014-03-11 11:47 -0700
      Re: c prog -plz explain glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-11 21:41 +0000
        Re: c prog -plz explain Kaz Kylheku <kaz@kylheku.com> - 2014-03-11 22:01 +0000

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