Undefined reference to 'fmod'

James Stevenson wrote:

> > > No, fmod() is in libm, so you have to add -lm
to the link command.
> > >
> > > As a general rule, anything which uses
<math.h> has to link against
> > > libm.
> > 
> > Interesting.  Compiling with the argument -lm
fixed my problem.  That
> > leads me to another question: why are the
functions found in math.h in a
> > separate library?  I would have thought that all
functions found in the
> > standard C library would be in glibc (The K&R
book I'm reading said that
> > math.h is a part of the standard library.)
> 
> It cant be not all processors have floating point
unit's Therefor it cannot
> be in the main standard libary

There are some functions in libc which use floating-point.
Also, FP is
part of the C language itself; on processors which don't
support FP in
hardware, you just emulate it.

The reason for the use of a separate math library is more
likely to be
so that you can have different versions for systems with and
without
FP support. Implementing FP math functions using an FP
emulation
library is likely to be more efficient that relying upon
generic FP
emulation.

Generic FP emulation normally works by handling
"illegal instruction"
exceptions, which occur if a CPU without FP support attempts
to
execute a FP instruction. The exception handler then
emulates the
instruction in software. Exception handling normally adds
significant
overhead, so it's more efficient to replace FP instructions
with calls
to functions in an FP emulation library.

-- 
Glynn Clements <glynngclements.plus.com>
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