Date: Wed, 12 Apr 2006 01:21:56 +0200 From: Erik Trulsson <ertr1013@student.uu.se> To: Jonathan Herriott <herriojr@gmail.com> Cc: freebsd-questions@freebsd.org, Nicolas Blais <nb_root@videotron.ca> Subject: Re: pow function working unexpectedly Message-ID: <20060411232156.GA64832@owl.midgard.homeip.net> In-Reply-To: <6a56d69c0604111607l5fba5939pfc6461a99a2ceab3@mail.gmail.com> References: <6a56d69c0604111554o587ce2c5ha1ff4ea20bbab0a4@mail.gmail.com> <200604111857.43171.nb_root@videotron.ca> <6a56d69c0604111607l5fba5939pfc6461a99a2ceab3@mail.gmail.com>
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On Tue, Apr 11, 2006 at 11:07:35PM +0000, Jonathan Herriott wrote:
> Question then. Why would it work when I don't use variables if I
> don't include the library? This question is just out of curiosity.
Because the compiler recognizes that pow() when called with only
constants as arguments can be calculated at compile-time and does so.
If you look at the generated assembler you will see that there is no
call to pow() actually being made there -- it has been replaced by
the appropriate constant.
>
>
> On 4/11/06, Nicolas Blais <nb_root@videotron.ca> wrote:
> > On Tuesday 11 April 2006 18:54, Jonathan Herriott wrote:
> > > I just want to make sure I'm not being stupid before I send in a bug.
> > > The problem seems to be with gcc when using the pow function in the
> > > math.h library. Here's code that works:
> > >
> > > #include <stdio.h>
> > > #include <math.h>
> > >
> > > int main()
> > > {
> > > printf("%f\n", pow(2,3));
> > > return 0;
> > > }
> > >
> > >
> > > Now, the following will not compile:
> > >
> > > #include <stdio.h>
> > > #include <math.h>
> > >
> > > int main()
> > > {
> > > int x = 2; // I tried these as doubles too since the pow function
> > > takes doubles
> > > int y = 3;
> > >
> > > printf("%f\n", pow(x,y));
> > > return 0;
> > > }
> > >
> > > I compiled both programs using:
> > > gcc test.c
> > >
> > > The second example gives the following error:
> > >
> > > /var/tmp//ccxtkMwv.o(.text+0x45): In function `main':
> > > : undefined reference to `pow'
> > >
> > > If I comile with g++, I have no issues. Are these results that I
> > > should have? If so, why? If not, I'm going to submit the bug on gcc
> > > (or the linker, but I'm guessing it's the same group).
> > >
> > > Thanks,
> > > Jonathan Herriott
> >
> > gcc -lm test.c works. You forgot to include the math library.
> >
--
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se
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