Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sources.redhat.com/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sources.redhat.com/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com
Message-ID: <3D6D326F.6412C8E@princeton.edu>
Date: Wed, 28 Aug 2002 16:28:31 -0400
From: Cynthia Randles <crandles AT Princeton DOT EDU>
Organization: Princeton University
X-Accept-Language: en
MIME-Version: 1.0
To: cygwin AT cygwin DOT com
Subject: Re: cygwin gcc and arrays -- Possible bug???
References: <Pine DOT GSO DOT 4 DOT 44 DOT 0208281613140 DOT 23515-100000 AT slinky DOT cs DOT nyu DOT edu>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

I'll do that.  Thanks a lot for your help.

-Cynthia

Igor Pechtchanski wrote:
> 
> Cynthia,
> 
> On Wed, 28 Aug 2002, Cynthia Randles wrote:
> 
> > > Which libraries are you linking in?
> > #include <stdio.h>
> > #include <math.h>
> 
> Well, I actually meant the libraries specified to gcc on the command line,
> with the -l flag, but it's probably irrelevant in light of the other bug...
> 
> > > How are you allocating/declaring rad_array and vol_array?
> > #define NUMBINS (51 - 1)
> >
> > float rad_array[NUMBINS], vol_array[NUMBINS];
> >
> > > > I have the following lines of code:
> > > >
> > > >         for (i = 0; i <= NUMBINS; ++i)
> >
> > Please also check your loop limits - are you sure you wanted
> > > a '<=' there, rather than a '<'?
> 
> Here's that other bug I promised... :-)
> I deliberately put your loop limits next to your array declaration.
> Notice that the way you declared the arrays, they will have a valid range
> of indices from 0 to NUMBINS-1.  However, in the loop, the variable you
> use to index the arrays (i) will get up to NUMBINS.  Since the arrays are
> declared consecutively, the second (vol_array) is likely to follow the
> first (rad_array).  Therefore, writing into rad_array[NUMBINS] will
> likely write to vol_array[0].
> 
> From your output, it looks like you tested your code by setting NUMBINS to
> 0.  Therefore, you allocate two consecutive 0-sized arrays, and they will
> probably share the same space, which is why you get the output you get.
> 
> > Yes.  When I compile it with gcc on another machine, I get the right
> > results.
> 
> This is probably due to your luck and the fact that gcc does different
> alignment on different machines.  I'll venture to guess that "another
> machine" is not a PC...  In any case, you should either change your loop
> limits to avoid i==NUMBINS, or declare your arrays with size [NUMBINS+1],
> because as it stands, the code is incorrect.
>         Igor
> 
> On Wed, 28 Aug 2002, Cynthia Randles wrote:
> 
> > Dear Igor:
> >
> > Igor Pechtchanski wrote:
> > >
> > > Which version of gcc are you using?
> >
> > Well, since I just downloaded cygwin last week, I assume I have the
> > latest version of gcc.  I think it is gcc-2.95.
> >
> > > Which libraries are you linking in?
> > #include <stdio.h>
> > #include <math.h>
> >
> >
> > > How are you allocating/declaring rad_array and vol_array?
> > #define NUMBINS (51 - 1)
> >
> >  float rad_array[NUMBINS], vol_array[NUMBINS];
> >
> > >Is this a C or  C++ program?
> > C
> >
> > Please also check your loop limits - are you sure you wanted
> > > a '<=' there, rather than a '<'?
> >
> > Yes.  When I compile it with gcc on another machine, I get the right
> > results.
> >
> > If you have any ideas, please let me know.  Thanks for your help.
> >
> > Cynthia
> >
> >
> > > On Tue, 27 Aug 2002, Cynthia Randles wrote:
> > >
> > > > I was wondering if anyone could help me.
> > > > I have the following lines of code:
> > > >
> > > >         for (i = 0; i <=  NUMBINS; ++i)
> > > >         {
> > > >               printf("--------read in input files---------\n");
> > > >               printf("The value if i is %d\n", i);
> > > >               fscanf(ifp1, "%f\n", &radius_microns);
> > > >               fscanf(ifp2, "%f\n", &volfraction);
> > > >               printf("The value of radius is %f\n", radius_microns);
> > > >               rad_array[i]= radius_microns;
> > > >
> > > >               printf("The radius is rad_array[%d]=%f\n\n",i, rad_array[i]);
> > > >
> > > >               printf("The value of volfraction is %f\n", volfraction);
> > > >               vol_array[i] = volfraction;
> > > >               printf("The volfraction is vol_array[%d]=%f\n", i, vol_array[i]);
> > > >               printf("The value of rad_array[%i] is %f\n", i, rad_array[i]);
> > > >               printf("----------end of read in input file------\n\n");
> > > >         }
> > > >
> > > > which, in cygwin produces:
> > > >
> > > > --------read in input files---------
> > > > The value of i is 0
> > > > The value of radius is 0.200000
> > > > The radius is rad_array[0] = 0.200000
> > > >
> > > > The value of volfraction is 0.330000
> > > > The volfraction is vol_array[0]=0.330000
> > > > The value of rad_array[0] is 0.330000
> > > > ----------end of read in input file-----
> > > >
> > > > as you can see, for some reason rad_array[0] is being reassigned even
> > > > though I never ask for that!!!
> > > >
> > > > my red-hat linux gcc produces:
> > > >
> > > > --------read in input files---------
> > > > The value of i is 0
> > > > The value of radius is 0.200000
> > > > The radius is rad_array[0] = 0.200000
> > > >
> > > > The value of volfraction is 0.330000
> > > > The volfraction is vol_array[0]=0.330000
> > > > The value of rad_array[0] is 0.200000
> > > > ----------end of read in input file-----
> > > >
> > > > which is the right answer.  I cannot figure out what is going
> > > > on with cygwin, and I haven't found a post that can help me.  Any
> > > > help is appreciated.
> > > >
> > > > Thanks,
> > > > Cynthia
> 
> --
>                                 http://cs.nyu.edu/~pechtcha/
>       |\      _,,,---,,_                pechtcha AT cs DOT nyu DOT edu
> ZZZzz /,`.-'`'    -.  ;-;;,_            igor AT watson DOT ibm DOT com
>      |,4-  ) )-,_. ,\ (  `'-'           Igor Pechtchanski
>     '---''(_/--'  `-'\_) fL     a.k.a JaguaR-R-R-r-r-r-.-.-.  Meow!
> 
> It took the computational power of three Commodore 64s to fly to the moon.
> It takes a 486 to run Windows 95.  Something is wrong here. -- SC sig file

--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Bug reporting:         http://cygwin.com/bugs.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/