Undefined reference to `pow' and `floor'

Question

I'm trying to make a simple fibonacci calculator in C but when compiling gcc tells me that I'm missing the pow and floor functions. What's wrong?

Code:

#include <stdio.h> #include <math.h>  int fibo(int n);  int main() {         printf("Fib(4) = %d", fibo(4));         return 0; }  int fibo(int n) {         double phi = 1.61803399;          return (int)(floor((float)(pow(phi, n) / sqrt(5)) + .5f)); } 

Output:

gab@testvm:~/work/c/fibo$ gcc fib.c -o fibo /tmp/ccNSjm4q.o: In function `fibo': fib.c:(.text+0x4a): undefined reference to `pow' fib.c:(.text+0x68): undefined reference to `floor' collect2: ld returned 1 exit status 

Answer 1

You need to compile with the link flag -lm, like this:

gcc fib.c -lm -o fibo 

This will tell gcc to link your code against the math lib. Just be sure to put the flag after the objects you want to link.

Answer 2

Add -lm to your link options, since pow() and floor() are part of the math library:

gcc fib.c -o fibo -lm