math.h problem -> sqrt undefined

[LeTubs]

Hi

I'm having a bit of problem trying to compile
a program..... which uses math.h

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

double sxy, sxx, syyy;
..
..
..
..
r = sxy / sqrt( sxx * syyy );
When I compile I get undefined reference to 'sqrt'
now the funny thing is that I use the function abs
which is the math.h function. I'm sort of at a lose end
does anybody have any ideas ?

Thanks
David

[Jens.Toerring]

LeTubs <dl*****@yahoon ospam.co.uk> wrote:

I'm having a bit of problem trying to compile
a program..... which uses math.h #include <stdio.h>
#include <stdlib.h>
#include <math.h> double sxy, sxx, syyy;
.
r = sxy / sqrt( sxx * syyy ); When I compile I get undefined reference to 'sqrt'
now the funny thing is that I use the function abs
which is the math.h function. I'm sort of at a lose end
does anybody have any ideas ?

Have you read the FAQ? "Undefined reference" is always a linker,
not a compiler problem. You're not linking against the math
library. You probably need to add "-lm" to the command you use
for linking the program.
Regards, Jens
--
\ Jens Thoms Toerring ___ Je***********@p hysik.fu-berlin.de
\______________ ____________ http://www.toerring.de

[Eric Amick]

On Fri, 25 Jun 2004 01:41:46 +0100, "LeTubs" <dl*****@yahoon ospam.co.uk>
wrote:

When I compile I get undefined reference to 'sqrt'
now the funny thing is that I use the function abs
which is the math.h function. I'm sort of at a lose end
does anybody have any ideas ?

This is in the FAQ, though the FAQ might refer to a different function
in <math.h>. (abs is declared in <stdlib.h>, BTW.)

--
Eric Amick
Columbia, MD

[bq]

"LeTubs" <dl*****@yahoon ospam.co.uk> wrote in message news:<dpLCc.302 $da5.207@newsfe 2-win>...

now the funny thing is that I use the function abs
which is the math.h function.

If you want ablsoute values of floating point numbers use fabs(), not abs().
e.g. abs(5.3) is 5, the integer 5, and when you do
double x;
x = abs(5.3);
that integer get converted to double and you effectively get x = 5.0

bq