math.h doesn't seem to be working

Bethmo · 02-26-2008, 10:29 AM

Hello!
I am a new user of linux(although with a 4 year old distribution of Mandrake), and have a very small amount of c programming. Anyway I believe the function "sin" is part of math.h, but when I use the function gcc claims to not have heard of it. Similar for other math.h functions. So: Is there a problem with my math.h? Can I get a new one? Or am I just a deluded fool and sin shouldn't be in this header file at all?

Simon Bridge · 02-26-2008, 10:34 AM

if you include math.h you need to link in libm.a with the -lm option, vis:

gcc myprog.c -o myprog -lm

b0uncer · 02-26-2008, 10:35 AM

If I remember it right, you have to use the command line switch '-lm' when including math.h.

Code:

gcc -lm yourcode.c

Bethmo · 02-26-2008, 01:05 PM

Thats absolutely brilliant.

Err...do I have to do this with any other header files? Also why do I have to? Is there some kind of internetland place I can go to to read this?

Wim Sturkenboom · 02-26-2008, 01:22 PM

You have to do this when the function is not in the standard library; that's however not for every include file the case (e.g functions in stdio.h do not need an additional to be linked).

Unfortunately I can not tell you where to find the info.

PS
Just in case you want to ask more programming related questions in the future:
there is a dedicated programming section at LQ that's better suited for programming related questions.