Undefined reference to sqrt (or other mathematical functions)

Question

I have this simple code:

max = (int) sqrt (number);

and in the header I have:

#include <math.h>

But application still says undefined reference to sqrt. Do you see any problem here? It looks like everything should be okay.

Answer 1

I suppose you have imported math.h with #include <math.h>

So the only other reason I can see is a missing linking information. You must link your code with the -lm option.

If you're simply trying to compile one file with gcc, just add -lm to your command line, otherwise, give some informations about your building process.

Answer 2

Just adding the #include <math.h> in c source file and -lm in Makefile at the end will work for me.

    gcc -pthread -o p3 p3.c -lm

Answer 3

Here are my observation, firstly you need to include the header math.h as sqrt() function declared in math.h header file. For e.g

#include <math.h>

secondly, if you read manual page of sqrt you will notice this line Link with -lm.

#include <math.h> /* header file you need to include */

double sqrt(double x); /* prototype of sqrt() function */

Link with -lm. /* Library linking instruction */

But application still says undefined reference to sqrt. Do you see any problem here?

Compiler error is correct as you haven't linked your program with library lm & linker is unable to find reference of sqrt(), you need to link it explicitly. For e.g

gcc -Wall -Wextra -Werror -pedantic test.c -lm

Answer 4

I had the same issue, but I simply solved it by adding -lm after the command that runs my code. Example. gcc code.c -lm