why sqrtf doesn't accept a variable as argument in debian or ubuntu?

Question

I want work with this function and it will take a variable as argument but is not working with me. If i put the number it works but a number in argument does not work.

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

int main(void)
{
  float x;
  x = 7;
  printf("%f", sqrtf(x)); // produces error "undefined reference to `sqrtf'"
}

int main(void)
{
   printf("%f", sqrtf(7)); // works
}

Did you link in the math library, i.e. the `-lm` option to gcc? — dbush, Jan 18 '22 at 22:16
no ididnt actually it is should just compile like this ```gcc -lm .c```? — Aitbelhaj Ayoub, Jan 19 '22 at 23:37

0___________ · Accepted Answer · 2022-01-18T22:38:09.140

3

sqrtf(7) is evaluated compile time and sqrtf function is not called. (it "works")
sqrtf(x) is evaluated run time and sqrtf function is called. (it does not "work" - ie it does not link) https://godbolt.org/z/oY6zfqxd1

You need to add -lm compile option to link against the math library. If you do not, the program will not link.

edited Jan 18 '22 at 22:38

answered Jan 18 '22 at 22:17

0___________

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@AitbelhajAyoub Also, if you're feeling adventuresome, file a bug report with your compiler vendor. You should not (IMHO) need to explicitly specify `-lm` to get a standard library function. – Steve Summit Jan 18 '22 at 22:27
@SteveSummit did you fill the gcc bugzilla error report? :) – 0___________ Jan 18 '22 at 22:34
No, but I really should, since I complain/whine/flame about the issue enough. – Steve Summit Jan 18 '22 at 22:38
Read [Why do you have to link the math library in C?](https://stackoverflow.com/q/1033898/10077). – Fred Larson Jan 18 '22 at 22:41
its work my brother thank you so mush @0___________ – Aitbelhaj Ayoub Jan 19 '22 at 23:48

why sqrtf doesn't accept a variable as argument in debian or ubuntu?

1 Answers1