[FIXED] Undefined reference to 'pow', 'floorf' and 'floor'

In this article, we have presented 3 ways to fix the error "Undefined reference to 'pow', 'floorf' and 'floor'" while compiling C programs.

Table of contents:

1. Error
2. Fix 1: Include math.h
3. Fix 2: Add flag -lm
4. Fix 3: Use LD_PRELOAD

Error

On compiling a C program, you may face any error as follows:

Command:

gcc code.c

Error:

opengenus.c:(.text+0x2a): undefined reference to 'pow'
opengenus.c:(.text+0x4a): undefined reference to 'floor'
opengenus.c:(.text+0x6a): undefined reference to 'floorf'

This can happen with other math functions as well like ceil.

opengenus.c:(.text+0x4a): undefined reference to 'ceil'

Fix 1: Include math.h

Make sure you have included math.h header file. Include it at the top of your C program as follows:

#include <math.h>

Fix 2: Add flag -lm

If you have included the header file, the issue is with your compilation command. You need to add the link flag -lm. It will link the math library.

gcc code.c

to

gcc code.c -lm

Important: Add the lm flag at the end.

Fix 3: Use LD_PRELOAD

The math library is named as libm.so and is usually, located in /lib or /usr/lib in UNIX system like Ubuntu. Go to these locations and try to locate libm.so.

Once you find it, add it to the environment variable LD_PRELOAD.

export LD_PRELOAD="/usr/lib/libm.so"

With these two fixes, the error should be fixed. Best of luck debugging.