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From:	Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: parsing errors
Date:	18 Mar 2002 11:19:06 GMT
Organization:	Aachen University of Technology (RWTH)
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A. Sinan Unur <asu1 AT cornell DOT edu> wrote:
[...]
> w.c:175:4: warning: pasting "new_alpha" and "[" does not give a valid 
> preprocessing token
[...]
> #define create_priori_angle( phi ) \
> new_##phi##[0]=phi##[0]+phi##[1]*delt;\
> new_##phi##[1]=phi##[1];\
> P_##phi##[0]+=.0001*delt;P_##phi##[2]+=.001*delt

> that just looks weird to me. 

It's not just weird, it's plain wrong.  GCC is correct to warn about this.

> why not use:

> #define create_priori_angle( phi ) \
>  new_##phi[0]=phi[0]+phi[1]*delt;  \
>  new_##phi[1]=phi[1];\
>  P_##phi[0]+=.0001*delt;P_##phi[2]+=.001*delt

That's the correct way of doing this, indeed. A slight improvement
would be:

#define create_priori_angle( phi ) do {\
 new_##phi[0]=phi[0]+phi[1]*delt;  \
 new_##phi[1]=phi[1];\
 P_##phi[0]+=.0001*delt;
 P_##phi[2]+=.001*delt;
} while(0)

This will allow things like

	if (condition)
	   create_priori_angle(alpha);
	else
	   create_priori_angle(beta);

to do what you thought they would, without restricting you to always
place { }.


-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.

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