Conditional Define

[Richard Bos]

Re: Conditional Define

"Paul Mensonides" <leavings@comca st.net> wrote:
[color=blue]
> Jack Klein wrote:[/color]

[ No, he didn't. Do not over-snip attributions. ]
[color=blue][color=green][color=darkred]
> >> Boost.Preproces sor can perform this operation in several ways.
> >> Here's one:
> >>
> >> #include <boost/preprocessor/comparison/greater.hpp>
> >> #include <boost/preprocessor/control/iif.hpp>[/color]
> >
> > And exactly what is that supposed to mean in comp.lang.c?[/color]
>
> Unlike the rest of Boost, Boost.Preproces sor is both a C and C++ library.[/color]

And is this Boost Preprocessor written in, and _completely_ compatible
with, ISO C? And is the source code readily available so we can check
this?

Richard

[Case]

Re: Conditional Define

Peter Nilsson wrote:[color=blue]
> Case <no@no.no> wrote in message news:<408d1816$ 0$571$e4fe514c@ news.xs4all.nl> ...[color=green]
>>#define FUNCT10() ...........
>>#define FUNCT20() ......
>>#define FUNCT56() .........
>>#define FUNCT.....
>>
>>#define FUNCT(x, y) FUNCT ## x (y)[/color]
>
>
> ITYM:
>
> #define FUNCT10 20
> #define FUNCT20 20
> #define FUNCT34 20
> #define FUNCT36 56
>
> #define CAT(x,y) x ## y
> #define FUNCT(x) CAT(FUNCT,x)
>
> FUNCT(10)
> FUNCT(20)
> FUNCT(34)
> FUNCT(36)
>
> #define A 36
> FUNCT(A)
>[/color]
Yep, that's more like it. Thanks for the addition, I was a
bit in a hurry yesterday.

Kees

[BQ]

Re: Conditional Define

"BQ" <caa_via_sto_to c_balulaz@APOCH ESTOlibero.it> ha scritto nel messaggio
news:ph5jc.2264 0$Qc.919215@twi ster1.libero.it ...[color=blue]
> Hello
> Is there a way to declare 'FUNCT' via a define so that if its parameter x, a constant,[/color]
is[color=blue]
> greater than 35, it returns 56, if not, 20.
> I would like that at compile time, not at run time.
> So:
> #define FUNCT(x) x>35?56:20
> is not the answer to my question.
> Could be something like
> #define FUNCT(x) #if (x>35) 56 #else 20 #endif
> Since the 'x' is a constant, this can be done by the preprocessor, so I suppose there's[/color]
a[color=blue]
> way to do it.
> Maybe it's a stupid question but is there a solution to this issue?
> Thank you in advance,
> Marco Lazzaroni[/color]

Thank you all for your useful replies that helped me in better understanding the
preprocessor.
After re-examining the problem many times I found out that it can be reduced to the need
of writing:

#define FUNCT(x) #if TEST(x) Y1(x) #else Y2(x) #endif

But as clearly stated in the FAQ, 10.14, the preprocessor can't be called on itself.

I have to use FUNCT(x) with about hundreds of different costant values for x. This
prevents the use of the interesting ## directive for reasons of readability and
re-usability of the code.
Obviously there are many ways to achieve what I need with smarter coding, without need of
macros. But my major issue is about code space and I can't choose this solution. So, since
I can't even rely on the compiler's efficiency - as considered in some of the posts - I
will write a small pre-preprocessor.

Thank you all again! :-)

Regards,
Marco Lazzaroni

[Peter Nilsson]

Re: Conditional Define

"Richard Bos" <rlb@hoekstra-uitgeverij.nl> wrote in message
news:408dfd41.2 415489051@news. individual.net. ..[color=blue]
> "Paul Mensonides" <leavings@comca st.net> wrote:[color=green]
> >[color=darkred]
> > >> #include <boost/preprocessor/comparison/greater.hpp>
> > >> #include <boost/preprocessor/control/iif.hpp>
> > >
> > > And exactly what is that supposed to mean in comp.lang.c?[/color]
> >
> > Unlike the rest of Boost, Boost.Preproces sor is both a C and C++ library.[/color]
>
> And is this Boost Preprocessor written in, and _completely_ compatible
> with, ISO C?[/color]

It's not strictly conforming (it exceeds various minimum implementation limits), but it's
close.
[color=blue]
> And is the source code readily available so we can check this?[/color]

Yes. www.boost.org

--
Peter

[ZAPPLE]

Re: Conditional Define

"BQ" <caa_via_sto_to c_balulaz@APOCH ESTOlibero.it> wrote in message news:<DMnjc.148 084$Kc3.4909378 @twister2.liber o.it>...[color=blue]
> "BQ" <caa_via_sto_to c_balulaz@APOCH ESTOlibero.it> ha scritto nel messaggio
> news:ph5jc.2264 0$Qc.919215@twi ster1.libero.it ...[color=green]
> > Hello
> > Is there a way to declare 'FUNCT' via a define so that if its parameter x, a constant,[/color]
> is[color=green]
> > greater than 35, it returns 56, if not, 20.
> > I would like that at compile time, not at run time.
> > So:
> > #define FUNCT(x) x>35?56:20
> > is not the answer to my question.
> > Could be something like
> > #define FUNCT(x) #if (x>35) 56 #else 20 #endif
> > Since the 'x' is a constant, this can be done by the preprocessor, so I suppose there's[/color]
> a[color=green]
> > way to do it.
> > Maybe it's a stupid question but is there a solution to this issue?
> > Thank you in advance,
> > Marco Lazzaroni[/color]
>
> Thank you all for your useful replies that helped me in better understanding the
> preprocessor.
> After re-examining the problem many times I found out that it can be reduced to the need
> of writing:
>
> #define FUNCT(x) #if TEST(x) Y1(x) #else Y2(x) #endif
>
> But as clearly stated in the FAQ, 10.14, the preprocessor can't be called on itself.
>
> I have to use FUNCT(x) with about hundreds of different costant values for x. This
> prevents the use of the interesting ## directive for reasons of readability and
> re-usability of the code.
> Obviously there are many ways to achieve what I need with smarter coding, without need of
> macros. But my major issue is about code space and I can't choose this solution. So, since
> I can't even rely on the compiler's efficiency - as considered in some of the posts - I
> will write a small pre-preprocessor.
>
> Thank you all again! :-)
>
> Regards,
> Marco Lazzaroni[/color]

Hi Guys,
I think the previous one is a very good example and explanation for your question
ZAPPLE