Re: undefined sqrt()

["Theo. Sean Schulze" <tschulze@teamfinders.org>]

Thanks.  The "-lm" did it.  Why?  I see from the gcc man page that the "-l" is a linker option.  Am I right that the linker then searches for "libm.a"?  Again, why, if I am right, would it need to after I included math.h?  Isn't sqrt() in math.h?

Thanks,
Sean

On Thu, Oct 24, 2002 at 04:17:27PM -0400, Karthik Vishwanath hunted and pecked out:
> Try:
> 
> gcc -Wall -lm -o glide glide.c
> 
> -K
> 
> ----------------------------------------
> The biggest difference between time and space is that you 
> can't reuse time -- Merrick Furst
> 
> 
> On Thu, 24 Oct 2002, Theo. Sean Schulze wrote:
> 
> > Hello,
> > 
> > This is a real newbie type question.  Usually my problems with C involve pointers, but this one is a problem with the function sqrt().  I had a math problem I needed to solve, and having forgotten my high school algebra about 25 years ago, I thought I could quickly write a C program to get an approximate answer by brute force.  This program is supposed to figure out one of the sides of a right triangle using the other side and the hypotenuse.  The hypotenuse has a fixed relationship to the side of unknown lenght.  Anyway, here is the code, such as it is:
> > 
> > 
> > //
> > // Filename: glide.c
> > // Version: 0.0.1     Date: 24 October, 2002
> > //
> > // Author: T. Sean Schulze
> > // System: i386-slackware-linux-gnu
> > //
> > // Purpose: The purpose of this script is to use brute force to find out
> > // how long the long side and the hypotenuse of a right triangle are 
> > // when the short side of the triangle is 35 feet long.  This will, of 
> > // course, vary depending on the angle between the two unknown sides.
> > //
> > // Limitations: Down and dirty.  Not useful for much else than this brute
> > // attempt.
> > 
> > #include <stdio.h>
> > #include <math.h>
> > #include <float.h>
> > #include <stdarg.h>
> > #include <stddef.h>
> > #include <stdlib.h>
> > #include <unistd.h>
> > #include <errno.h>
> > 
> > double a ;
> > double b ;
> > double c ;
> > double GLIDE ;
> > 
> > int
> > main(void) /*(int argc, char **argv)*/
> > {
> > 	GLIDE = 0.012 ;
> > 	a = 0.0 ;
> > 
> > 	while( b < 35.0 ) 
> > 	{
> > 		a++ ;
> > 		c = a * (1 + GLIDE) ;
> > 		b = sqrt((c * c) - (a * a)) ;
> > 
> > 	}
> > 	
> > 	printf("Glide = %f\n", GLIDE);
> > 	printf("a = %f\n", a) ;
> > 	printf("b = %f\n", b) ;
> > 	printf("c = %f\n", c) ;
> > 
> > 	exit(0);
> > 
> > }
> > 
> > When I try to compile it, I get these messages:
> > 
> > dragoon:/home/tschulze/bin # gcc -Wall -o glide glide.c
> > /tmp/ccXahjXY.o: In function `main':
> > /tmp/ccXahjXY.o(.text+0x98): undefined reference to `sqrt'
> > collect2: ld returned 1 exit status
> > 
> > Could someone please give me a hint why this doesn't work?
> > 
> > TIA,
> > Sean
> > 
> > -- 
> > Theo. Sean Schulze
> > tschulze@teamfinders.org
> > -
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> > 
> 

-- 
Theo. Sean Schulze
tschulze@teamfinders.org