Re: reasons for preferring C over C++

From	Stefan Reuther <stefan.news@arcor.de>
Newsgroups	comp.arch.embedded
Subject	Re: reasons for preferring C over C++
Date	2014-10-15 20:44 +0200
Message-ID	<m1mmar.23s.1@stefan.msgid.phost.de> (permalink)
References	<543ead04$0$15847$e4fe514c@dreader35.news.xs4all.nl>

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Wouter van Ooijen wrote:
> A student of me is looking for reasons that are put forward for
> preferring C over C++ on small chips. (Note: all reasons, not just
> *valid* reasons).
> 
> So far he found
> 
> - tooling & experience (no C++ available for my chip, no C++ experience)

That would be the killer argument for me. There is no point in reasoning
about using C++ if all you have for your chip is a C compiler. (And
there is no point in reasoning about using C if all you have is an
assembler and a crappy gcc 1.x.)

> - semantic distance to the machine code (I can't easily see what code
> this C++ construct will cause)

You can work as close or as far from the machine as you want. It just
takes much more experience in C++ than in C to know what language
constructs cost you what in terms of code and memory. I have written
boot loaders in C++ ("boot loader" as in "configure RAM and flash and
then get that image running ASAP", not "fancy shell prompt with menus
and file system and stuff over serial and TCP").

C's advantage here is that it's a WYSIWYG language: if you want bloated
code, you actually have to write it. In C++, you may get the bloat by
accident if you're not careful. On the other hand, you can write
hundreds of lines of code with dozens of (template) classes that don't
generate a single machine instruction.

A concrete instance of this problem is that it's easier to avoid needing
libraries in C. About the worst function call a C compiler will generate
implicitly is memcpy, memset, or things like long multiply. If you write
C++ as it's meant to be, with destructors and all, you'll easily get
functions into your code (exception handling) that you cannot simply
replace by a three-line *.asm file.

> - C++ stronger typing gets in the way (forces you to write lots of casts)

The only cast you need in C++ that you don't need in C is the
void*->something* cast. And you need fewer void*->something* conversions
in C++ than in C if you translate the "callback + void* pointer" idiom
into a "class with a virtual method".

The thing that gets bazillions of casts into your code is MISRA, not C++ :-)

> - the const trap (ultimately you might/will need to cast the cost away)

This applies to C as well. If you start using it (and you should), you
have to use it everywhere.

> - errors are harder to locate

Some C++ error messages are hard to decipher, but compilers are getting
better.

  Stefan

Thread

reasons for preferring C over C++ Wouter van Ooijen <wouter@voti.nl> - 2014-10-15 19:21 +0200
  Re: reasons for preferring C over C++ Paul Rubin <no.email@nospam.invalid> - 2014-10-15 10:36 -0700
    Re: reasons for preferring C over C++ Wouter van Ooijen <wouter@voti.nl> - 2014-10-15 19:48 +0200
      Re: reasons for preferring C over C++ Tom Gardner <spamjunk@blueyonder.co.uk> - 2014-10-15 21:25 +0100
        Re: reasons for preferring C over C++ Wouter van Ooijen <wouter@voti.nl> - 2014-10-15 23:28 +0200
          Re: reasons for preferring C over C++ Tom Gardner <spamjunk@blueyonder.co.uk> - 2014-10-15 23:40 +0100
  Re: reasons for preferring C over C++ Don Y <this@is.not.me.com> - 2014-10-15 10:58 -0700
  Re: reasons for preferring C over C++ upsidedown@downunder.com - 2014-10-15 21:03 +0300
    Re: reasons for preferring C over C++ Don Y <this@is.not.me.com> - 2014-10-15 11:11 -0700
    Re: reasons for preferring C over C++ Wouter van Ooijen <wouter@voti.nl> - 2014-10-15 20:26 +0200
  Re: reasons for preferring C over C++ Stefan Reuther <stefan.news@arcor.de> - 2014-10-15 20:44 +0200
    Re: reasons for preferring C over C++ Wouter van Ooijen <wouter@voti.nl> - 2014-10-15 23:30 +0200
      Re: reasons for preferring C over C++ Stefan Reuther <stefan.news@arcor.de> - 2014-10-16 18:19 +0200
        Re: reasons for preferring C over C++ Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2014-10-16 23:12 +0200
          Re: reasons for preferring C over C++ Reinhardt Behm <rbehm@hushmail.com> - 2014-10-17 13:25 +0800
          Re: reasons for preferring C over C++ Stefan Reuther <stefan.news@arcor.de> - 2014-10-17 18:43 +0200
    Re: reasons for preferring C over C++ "tim....." <tims_new_home@yahoo.co.uk> - 2014-10-18 12:29 +0100
      Re: reasons for preferring C over C++ Paul Rubin <no.email@nospam.invalid> - 2014-10-18 11:44 -0700
        Re: reasons for preferring C over C++ Tom Gardner <spamjunk@blueyonder.co.uk> - 2014-10-18 22:25 +0100
          Re: reasons for preferring C over C++ Paul Rubin <no.email@nospam.invalid> - 2014-10-18 15:42 -0700
            Re: reasons for preferring C over C++ Niklas Holsti <niklas.holsti@tidorum.invalid> - 2014-10-19 11:03 +0300
            Re: reasons for preferring C over C++ Tim Wescott <seemywebsite@myfooter.really> - 2014-10-19 17:46 -0500
              Re: reasons for preferring C over C++ Paul Rubin <no.email@nospam.invalid> - 2014-10-19 16:28 -0700
              Re: reasons for preferring C over C++ Nobody <nobody@nowhere.invalid> - 2014-10-20 02:47 +0100
        Re: reasons for preferring C over C++ "tim....." <tims_new_home@yahoo.co.uk> - 2014-10-19 09:34 +0100
          Re: reasons for preferring C over C++ Paul Rubin <no.email@nospam.invalid> - 2014-10-19 17:00 -0700
            Re: reasons for preferring C over C++ Tom Gardner <spamjunk@blueyonder.co.uk> - 2014-10-20 08:50 +0100
              Re: reasons for preferring C over C++ "tim....." <tims_new_home@yahoo.co.uk> - 2014-10-20 11:57 +0100
                Re: reasons for preferring C over C++ Tom Gardner <spamjunk@blueyonder.co.uk> - 2014-10-20 12:11 +0100
                Re: reasons for preferring C over C++ upsidedown@downunder.com - 2014-10-20 22:36 +0300
                Re: reasons for preferring C over C++ Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2014-10-21 00:36 +0000
            Re: reasons for preferring C over C++ Tom Gardner <spamjunk@blueyonder.co.uk> - 2014-10-20 08:52 +0100
            Re: reasons for preferring C over C++ "tim....." <tims_new_home@yahoo.co.uk> - 2014-10-20 11:56 +0100
        Re: reasons for preferring C over C++ Stefan Reuther <stefan.news@arcor.de> - 2014-10-19 10:52 +0200
          Re: reasons for preferring C over C++ Paul Rubin <no.email@nospam.invalid> - 2014-10-19 17:16 -0700
      Re: reasons for preferring C over C++ glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-10-18 23:02 +0000
        Re: reasons for preferring C over C++ "tim....." <tims_new_home@yahoo.co.uk> - 2014-10-19 09:45 +0100
  Re: reasons for preferring C over C++ David Brown <david.brown@hesbynett.no> - 2014-10-15 22:12 +0200
    Re: reasons for preferring C over C++ Wouter van Ooijen <wouter@voti.nl> - 2014-10-15 23:35 +0200
      Re: reasons for preferring C over C++ Paul Rubin <no.email@nospam.invalid> - 2014-10-15 19:10 -0700
      Re: reasons for preferring C over C++ Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2014-10-16 10:34 +0300
        Re: reasons for preferring C over C++ Tom Gardner <spamjunk@blueyonder.co.uk> - 2014-10-16 10:10 +0100
  Re: reasons for preferring C over C++ Tim Wescott <tim@seemywebsite.com> - 2014-10-16 01:06 -0500
  Re: reasons for preferring C over C++ Anders.Montonen@kapsi.spam.stop.fi.invalid - 2014-10-16 08:32 +0000
    Re: reasons for preferring C over C++ David Brown <david.brown@hesbynett.no> - 2014-10-16 20:54 +0200

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