Single line conditional compiles

Single line conditional compiles

[Gerrit van Niekerk]

How can one implement single line conditional compile macros with GCC? 

Instead of having:

#ifdef OPT1
<valid C line>
#endif

Having something like:
IFOPT1 <valid C line>

The following works with BorlandC, but not GCC:

#ifdef OPT1
#define IFOPT1
#else
#define IFOPT1 /##/
#endif

I understand why it does not work - I am looking for a solution, not an 
explanation :)

===============================================
Gerrit van Niekerk
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===============================================

Re: Single line conditional compiles

[random]

Gerrit van Niekerk wrote:

>How can one implement single line conditional compile macros with GCC? 
>
>Instead of having:
>
>#ifdef OPT1
><valid C line>
>#endif
>
>Having something like:
>IFOPT1 <valid C line>
>
>The following works with BorlandC, but not GCC:
>
>#ifdef OPT1
>#define IFOPT1
>#else
>#define IFOPT1 /##/
>#endif
>
>I understand why it does not work - I am looking for a solution, not an 
>explanation :)
>
>  
>
Not quite what you are looking for, but how about?

#ifdef OPT1
#define IFOPT1(x) x
#else
#define IFOPT1(x)
#endif

Then you write
IFOPT1(stuff)

This has the advantage you can write it mid-line, with stuff before and
after it.

Chris

Re: Single line conditional compiles

[Eljay Love-Jensen]

Hi Gerrit,

> I understand why it does not work - I am looking for a solution, not an
explanation :)

Well, that's good, because you saved me time explaining.  :-)

One solution is to run the preprocessor twice.

The first time it does all the normal preprocessor things (pulling in the
#include, expanding macros, yada yada yada), including embedding those
now-invalid comments into the post-preprocessed output.

The second time removes those introduced comments.

Voila!

--Eljay

Re: Single line conditional compiles

[Gerrit van Niekerk]

On 28 Jul 2005 at 17:07, random@bubblescope.net wrote:

> Gerrit van Niekerk wrote:
> 
> >How can one implement single line conditional compile macros with GCC? 
> >
> >Instead of having:
> >
> >#ifdef OPT1
> ><valid C line>
> >#endif
> >
> >Having something like:
> >IFOPT1 <valid C line>
> >
> >The following works with BorlandC, but not GCC:
> >
> >#ifdef OPT1
> >#define IFOPT1
> >#else
> >#define IFOPT1 /##/
> >#endif
> >
> >I understand why it does not work - I am looking for a solution, not an
> >explanation :)
> >
> >  
> >
> Not quite what you are looking for, but how about?
> 
> #ifdef OPT1
> #define IFOPT1(x) x
> #else
> #define IFOPT1(x)
> #endif
> 
> Then you write
> IFOPT1(stuff)
> 
> This has the advantage you can write it mid-line, with stuff before and
> after it.
> 
> Chris

Thanks Chris,

This is a workable solution and portable too!

Gerrit