Need to use extra option while compiling c code which includes <math.h>

Question

Whenever I include math.h to my c code I can't compile without the -lm option. I get this error message:

d.o: In function `refresh_position':
d.c:(.text+0x4df): undefined reference to `sqrt'
d.c:(.text+0x524): undefined reference to `sqrt'
collect2: error: ld returned 1 exit status

I can compile it with just typing -lm but my teacher says that if code doesn't work i will get 0 point from that homework. I want to know is this error occurs because of my code or because of my computer or c library. I have to be sure about it will run without any error on my teachers computer.

Answer 1

Some implementations such as gcc do not link the math library (called libm.a on most *nix implementations) by default, which is why you need to include the -lm when building the code.

Your teacher should be aware of issues like this, and as long as your code is using sqrt and other math routines correctly (using the right type for the inputs and output), he or she should be able to build your code such that it will run.