Strange compilation issue with gcc

Question

Why does the following program compile with gcc, ...

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

void foo(double x) {
   printf("%f", sin(2));
}

int main() {
   foo(1);
}

... while this other program doesn't?

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

void foo(double x) {
   printf("%f", sin(x));
}

int main() {
   foo(1);
}

It gives the following error message:

/tmp/ccVT7jlb.o: nella funzione "foo":
fun.c:(.text+0x1b): riferimento non definito a "sin"
collect2: error: ld returned 1 exit status*

Are you using the -lm option when compiling both executables? — wolfPack88
– wolfPack88, Commented Feb 19, 2015 at 22:58
@wolfPack88 No, I wasn't. I thought standard libraries were automatically linked. Now it works, thanks! — Matteo
– Matteo, Commented Feb 19, 2015 at 23:01
The first one doesn't actually have to link in the math library, because it can optimize sin(2) into a constant. The second one needs to load the sin() function, so you have to tell it to link to libm (or whatever your platform's equivalent is). — Lee Daniel Crocker
– Lee Daniel Crocker, Commented Feb 19, 2015 at 23:08

Iharob Al Asimi · Accepted Answer · 2015-02-19 23:01:24Z

2

You need to link to libm.so like this

gcc -Wall -Wextra -Werror source.c -o executable -lm

see the -lm

answered Feb 19, 2015 at 23:01

Iharob Al Asimi

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1 Comment

Also make sure it's the last option.