Using math.h sqrt function in C

Question

Reading the documentation for math.h, it seems like all I should have to do is include math.h, and use the math functions included, such as sqrt. The problem is I get the following error when trying to use sqrt in my program. I tried math.sqrt, but that did not work, either. Any idea what I am doing wrong?

undefined reference to `sqrt'

...

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

int main (int argc, char *argv[])
{
  int a, b;

  a = 1;
  b = 5;

  if (a < sqrt (b))
    printf("1 < sqrt(5)");

  return 0;
}

I know it says `sin`, but it's the same for any math function. — hammar, May 16 '13 at 00:05

score 5 · Accepted Answer · answered May 16 '13 at 00:03

5

You need to explicitely link with the math library as sqrt depends on it. Retry with appending -lm to your compilation line :

gcc you_file.c -o my_sqrt -lm

answered May 16 '13 at 00:03

Halim Qarroum

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2

Why does this library need to be explicitely linked when others don't? – LazerSharks Jun 25 '14 at 23:51
Nevermind, found the answer: http://stackoverflow.com/questions/4606301/gcc-why-the-lm-flag-is-needed-to-link-the-math-library – LazerSharks Jun 25 '14 at 23:52

Using math.h sqrt function in C

1 Answers1

Linked