Path: utzoo!attcan!utgpu!watmath!watdragon!dvadura
From: dvadura@watdragon.waterloo.edu (Dennis Vadura)
Newsgroups: comp.lang.c++
Subject: Re: Efficiency of C++ relative to C??
Message-ID: <16557@watdragon.waterloo.edu>
Date: 21 Sep 89 15:00:53 GMT
References: <16493@watdragon.waterloo.edu> <9924@alice.UUCP>
Reply-To: dvadura@watdragon.waterloo.edu (Dennis Vadura)
Organization: Computer Science Dept., University of Waterloo
Lines: 53

In article <9924@alice.UUCP> shopiro@alice.UUCP (Jonathan Shopiro) writes:
>In article <16493@watdragon.waterloo.edu>, dvadura@watdragon.waterloo.edu (Dennis Vadura) writes:
>> questions deleted...
>> 
>Yes, virtual functions are more expensive than ordinary functions
>(about 4 or 5 more memory references per call), but you don't have to
>use virtual functions if they aren't needed.
>...
>In your question you assume ``the full power of C++.''  Clearly if you
>use every feature wherever it could fit (for example, make every
>function and base class virtual), you could take a performance hit,
Yes but..., The original motivation for my question was from the standpoint
of using a lot of general classes in my implementation (although I didn't
say that).

In this case if the class designer was opting for maximum flexibility,
generality and reusability then it is my feeling they end up
using virtual functions a lot.  Not only that, but it is my
understanding that you end up designing a lot of classes to use virtual
inheritance so that if you inherit a class twice you only get a single
copy of the class.  I'm not completely clear on this as yet, but this
appears to incur further costs.

>always have written the same program in assembler.  That is to say, if
>you're considering higher level languages at all, performance is not
>your only criterion, you're also concerned about programmer productivity.
I agree whole heartedly.  Infact I have a language in mind where
almost all expressions translate into function invocations and the
implementation mechanism forces these to be indirect references through
a pointer.  The implementation takes a pretty severe hit on performance,
but the great expressive power of the language outweighs this somewhat.
That is why I am curious how much of a performace hit people are willing
to live with.

>programming large applications is too expensive, then try C++.  You
>will be able to build more complicated applications than you could
>before, and, if you program carefully, you will not incur any
>performance penalty.
Sorry I disagree.

   Theorem:
   I can write in C anything I write in C++, it might just
   take longer.

   Proof:
   cfront generates C as output.  I can type it in :-)

-dennis
-- 
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The only happy people are Single MEN   |Dennis  UUCP,BITNET:    dvadura@water
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