Proposal

[Neil Booth]

Frank Klemm wrote:-

> For instance you have a program which uses _ in numbers. 
> But not all compilers will will support this in the beginning.

Sure.

> It should be possible to write a program which removes these _ inside of
> numbers to allow to compile such source files with other compilers.

If the _'s aren't already in your source code, I don't see much point
putting them there with macros.  Wasn't the whole idea legibility?

> Without this rule it is impossible to write such a program without
> preprocessing the source file. And preprocessed files are no source files
> anymore.

Well, you might be able to filter it through sed or something, with a
little difficulty.

> To prevent this it is forbidden to use this feature in conjunction with
> token concatenation. At least as long as this is not an ISO standard.
> 
> For instance try to convert 
> 
>    #define MILLION	MY_MERGE_5 ( 1, _, 000, _, 000 )
> 
> to the old representation. Note that MY_MERGE_5 is a self defined macro.

I don't know what you mean by a self-defined macro.  I don't
understand why you're using macros (see comment above).  I'm not even
sure what the definition of MY_MERGE_5 is, though I might guess.

Anyway, if you insist on macros, you could get what you want through
an extra indirection, and an extra macro

#if COMPILER_UNDERSTANDS_EXTENDED_NUMBERS
#define UNDERSCORE _
#else
#define UNDERSCORE
#endif

#define MY_MERGE_5_INDIRECT (a, b, c, d, e) MY_MERGE_5 (a, b, c, d, e)
#define MILLION	MY_MERGE_5_INDIRECT (1, UNDERSCORE, 000, UNDERSCORE, 000)

But I really can't see the point here.

Neil.