TITLE: namespaces and cxxxx header files

(Newsgroups: comp.lang.c++.moderated, 9 Apr 97)

GANI: Tanveer Gani <tanveerg@microware.com>

[...]

>|> 3. In general, are the contents of <cxxxxx> headers to be
>|>    wrapped in namespace std { } ?
>|>

VANDEVOORDE: David Vandevoorde

>>    Yes. (Modulo certain things that are sometimes implemented
>>    as macros, if I remember well.)


KANZE: James Kanze <james-albert.kanze@vx.cit.alcatel.fr>

>What things?  According to the C standard: *any* of the functions may be
>implemented as a macro.  Note however:
>
>	#include <cctype>
>
>	if ( isalpha( c ) )             //  legal if macro, illegal if function
>	if ( std::isalpha( c ) )        //  legal if function, illegal if macro


CLAMAGE: Stephen.Clamage@Eng.Sun.COM (Steve Clamage)

Partly correct. According to the C standard (7.1.7 Use of Library
Functions), any function may be *additionally* implemented as a macro.
The functions must in all cases be implemented as functions, and
you can force a reference to the actual function by #undef-ing
the macro or by enclosing the function name in parens.

Example C code:
	#include <ctype.h>
	isalpha(c)	/* might be a macro */
	(isalpha)(c)	/* calls the function */
	#undef isalpha	/* allowed even if isalpha is not a macro */
	isalpha(c)	/* cannot now refer to a macro */

The C++ standard (in 17.3.1.2 Headers) forbids the implementation of
C library functions as macros. A C++ version of a C header should
make functions inline that would otherwise be macros.