How to use sqrt() function with gcc?

[John]

I'm trying to use the sqrt() function in Linux with GCC v3.3.6,
compiling with this command:
$ gcc sourcefile.c

I get this error:
In function 'main': undefined reference to 'sqrt'
collect2: ld returned 1 exit status

Here is my source code:
#include <stdio.h>
#include <math.h>
main()
{
double num, sq_double;
scanf("%d", &num);
sq_double = sqrt(num);
}

What am I doing wrong? Is there something special I need to do to use
the math.h functions?

[MrDev]

Try
gcc -lm sourcefile.c

John wrote:

I'm trying to use the sqrt() function in Linux with GCC v3.3.6,
compiling with this command:
$ gcc sourcefile.c

I get this error:
In function 'main': undefined reference to 'sqrt'
collect2: ld returned 1 exit status

Here is my source code:
#include <stdio.h>
#include <math.h>
main()
{
double num, sq_double;
scanf("%d", &num);
sq_double = sqrt(num);
}

What am I doing wrong? Is there something special I need to do to use
the math.h functions?

[Richard Heathfield]

John said:

I get this error:
In function 'main': undefined reference to 'sqrt'
collect2: ld returned 1 exit status

<snip>

scanf("%d", &num);

%lf for double. %d is for ints.

sq_double = sqrt(num);
}

What am I doing wrong? Is there something special I need to do to use
the math.h functions?

For gcc, yes, you need to tell it to link the math library in, by adding -lm
at the end of your gcc call.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Keith Thompson]

John <us**@home.netwrites:

I'm trying to use the sqrt() function in Linux with GCC v3.3.6,
compiling with this command:
$ gcc sourcefile.c

I get this error:
In function 'main': undefined reference to 'sqrt'
collect2: ld returned 1 exit status

[...]

<http://www.c-faq.com/>, question 14.3.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.