Path: utzoo!attcan!uunet!crdgw1!uakari.primate.wisc.edu!zaphod.mps.ohio-state.edu!swrinde!ucsd!ucbvax!bloom-beacon!mintaka!spdcc!ima!mirror!howtek!cory
From: cory@howtek.UUCP (Cory Kempf)
Newsgroups: comp.lang.c++
Subject: Re: FORever
Message-ID: <1537@howtek.UUCP>
Date: 3 Oct 90 15:12:35 GMT
References: <1990Sep27.150948.9109@sco.COM>
Reply-To: cory@howtek.UUCP (Cory Kempf)
Organization: Howtek Inc., Hudson, NH
Lines: 46

In article <1990Sep27.150948.9109@sco.COM> ron@sco.COM (Ron Irvine) writes:
>
>BEWARE there is a major problem with C++'s "for" statement.

No, the for statement works as it should...

>main() {
>	for (int i=10; i<13;) {
>		for (int i=0; i<3; ++i)
>			; // stuff
>		++i;
>	}
>}
>
>Cfront accepts this code and compiles without warning.
>The resulting code is totally unexpected!

hardly.  see below.  I will try to refrain from comment about
poor programming style.

>The program loops forever?!!

Of course it loops forever!  That is what you told it 
to do.  Think about how that structure would be implimented
in C:

  main() {
    int i;
    for(i=10;i<13;) {
      int i;	    // hides previous i
      for (i=0; i<3; ++i)
	    ; // stuff
      ++i;		// note the scope of i
    }
  }

The result is, I believe, obvious.

>I realize the problem is that cfront does not end the
>scope of the inners loop's "i" until the end of the
>outer loop, thus the "++i;" statement actually increments
>the inner loops "i" whos scope is the outer loop.  

This is a documented behaviour by the way.  

+C