Some questions about POSIX headers

[Bob Goudreau]

In article <6622 at portia.Stanford.EDU> karish at forel.stanford.edu (Chuck Karish) writes:
>
>    Under ANSI C, _LOW, _HIGH, __s, and __v are all reserved to the
>    library implementor if they're external identifiers, because they
>    all start with underscores.  In any standard header, they'll
>    become externals when the header is #included with external scope.
>
>    The question now becomes, is the header part of the library
>    implementation or not?  If any compiler other than the native one
>    will use these headers, the answer had best be `not'.
>
>    These identifiers are OK with file scope or smaller inside a C
>    library implementation, but not as external identifiers.

Here's what the Dec. 7, 1988 ANSI draft says about the matter:

	4.1.2.1  Reserved Identifiers

	Each header declares or defines all identifiers listed in its
	associated section, and optionally declares or defines
	identifiers listed in its associated future library directions
	section and identifiers which are always reserved either for
	any use or for use as file scope identifiers.

	+  All identifiers that begin with an underscore and either an
	   upper-case letter or another underscore are always reserved
	   for any use.

	+  All identifiers that begin with an underscore are always
	   reserved for use as identifiers with file scope in both the
	   ordinary identifier and tag name spaces.

	....


Since _LOW, _HIGH, __s and __v all fall into the first category ("always
reserved for any use"), the implementation is free to do what it wants
with them.  But note that if _s had been used instead of __s, only the
second category would have applied.

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