C program compilation error: undefined reference

Question

I am unable to compile the following simple C code and I don't know why.

#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <math.h>
int main(){
     double result;
     result = cos(0.5);
     printf("asin(0.5) is %f\n", result);
     return 0;
}

The error message I receive after I try to compile is -

In function 

'main':
test.c:(.text+0xlc): undefined reference to 'cos'
collect2: ld

 returned 1 exit status

Btw, I hope you noticed that you're calculating a cosine, and saying the result is the arc-sine, which are not the same thing. — R. Martinho Fernandes
– R. Martinho Fernandes, Commented Jul 17, 2011 at 19:24
This is actually a linker error rather than a compiler error. That is made clear because the error is coming from ld, the linker. Invariably the reason is a missing import library. — David Heffernan
– David Heffernan, Commented Jul 17, 2011 at 19:26

cnicutar · Accepted Answer · 2011-07-17 19:22:05Z

14

You need to link with the math library (-lm).

gcc -Wall -Wextra -o test test.c -lm

See this C FAQ.

answered Jul 17, 2011 at 19:22

cnicutar

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Comments

peeyush · Accepted Answer · 2011-07-17 20:07:06Z

0

In general whenever you get undefined reference error it's due to the compiler is not able to find your function definition. So it may be your function ( and you have not typed the spelling of function correctly so you will get this error ) or may be built-in function like you have encountered in this case.
to explore there are various library and their linking are necessary at the time of compilation

whenever you use math function use -lm ( l stands for link and m is for math )
in pthread built-in functions use -lpthread
and so on ... In this case indeed use -lm

gcc -lm test.c

will be able to compile your program .

answered Jul 17, 2011 at 20:07

peeyush

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