Re: [avr-gcc-list] Undefined reference - Why?

[Klaus Rotter]

On Sun, Mar 04, 2001 at 04:05:27PM +0100, Bernt Hustad Hembre wrote:
> #include <math.h>
> void  a_function(int tall);
> int main(void){       
>       int      hoyde;
>       double trykk;
> 
>       hoyde           = pow(2,2);
>       a_function(hoyde);
> //    trykk = hoyde * 1.234;
>       return 0;
> } /* main */
>       
> void  a_function(int tall){
> }

> M:\prosjekt\tuger\hw\firmware/tuger.c:10: undefined reference to `pow'

> But if I change this:
>       a_function(hoyde);
> //    trykk = hoyde * 1.234;
> to this:
> //    a_function(hoyde);
>       trykk = hoyde * 1.234;
> It compiles without any errormessages...

What do you expect ? You are compiling with -O3. If you comment out
a_function(hoyde) the optimzer recognices that hoyde and trykk are
calculated but _never_ used. So they will be optimized out. Compile this
withou any optimization and you get what you expected. You can also try
"return hoyde" instead of "return 0". 

-- 
 Klaus Rotter * mailto:address@hidden