Why am I getting this error when trying to use log from math.h in C? [duplicate]

Question

This question already has answers here:

Why do you have to link the math library in C? (14 answers)

Closed 8 years ago.

I need to use logs in a program for an assignment. I ran this test program on my machine to see how the log function works (and if it would), and I get the following error during build.

Code

/* log example */
#include <stdio.h>      /* printf */
#include <math.h>       /* log */

int main()
{
  double param, result;
  param = 5.5;
  result = log (param);
  printf ("log(%f) = %f\n", param, result );
  return 0;
}

ERROR

gcc -Wall -o "test" "test.c" (in directory: /home/linux/Development/codetest)
/tmp/ccCDqX7x.o: In function `main':
test.c:(.text+0x1b): undefined reference to `log'
collect2: ld returned 1 exit status
Compilation failed.

Link

This is C99 code, grabbed from this tutorial site.

Answer 1

Add -lm to your compilation command to link in the math library.

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