Re: ctype.h macros may conflict with C++11 UDL

Corinna Vinschen <[email protected]> Wed, 10 Oct 2018 12:59:13 +0200

Newsgroups	gmane.comp.lib.newlib
Message-ID	<[email protected]>

On Oct  9 18:03, Glenn Elliott wrote:
> Hello newlib maintainers,
> 
> ctype.h “#define"s the following values: _U, _L, _N, _S, _P, _C, _X, and _B.
> 
> These macros may conflict with C++11 user defined literals (UDL) (https://en.cppreference.com/w/cpp/language/user_literal <https://en.cppreference.com/w/cpp/language/user_literal>).  It’s easy to see how C++11 UDL suffixes might conflict it the macros defined in ctype.h.  For instance, one may define a UDL function of “_N” to instantiate a C++ type that represents newtons of force.  Indeed, this is done by this units library: https://github.com/nholthaus/units <https://github.com/nholthaus/units>
> 
> Must these macros leak from ctype.h?

Yes, they have to, otherwise the isXXX ctype macros can't be resolved
successfully.  Am I the only one thinkiong it was a bit non-considerate
of the C++ standarization commitee to use the underscore in a way 
potentially colliding with implementation-defined symbols.

Probably the most feasible workaround is to change those macros to
double underscores throughout.

Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat

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