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

 

[Richard Heathfield]

John said:

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

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.

 

[Keith Thompson]

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.