[Cfp-interest 2812] Action items about WANT macros in TS-4r

[Jim Thomas]

Action items from the 2 August CFP meeting:

>     Jim: Be consistent with the rest of the standard for section 5.3 in the TS (the "if and only if" part).
>     All: Consider weakening "if and only if" to "if" to allow more implementation latitude. Comes with the cost of being less consistent with the rest of the standard.
> 

cfp4r 5.3 says:

The types and functions whose definitions or declarations are specified in this document are defined or declared by the <math.h> headers if and only if __STDC_WANT_IEC_60559_FUNCS_EXT__ is defined as a macro at the point in the source file where the header is first included.

The issue was whether “if and only if” should be replaced by “if”. The WANT macros in the standard are

__STDC_WANT_IEC_60559_EXT__
__STDC_WANT_LIB_EXT1__
__STDC_WANT_IEC_60559_TYPES_EXT__

It’s usual in the standard for library interfaces conditioned by these WANT macros to be defined or declared only if the WANT macro is appropriately defined by the user. The reason is namespace protection, and WG 14 members have expressed significant interest in namespace protection. I think we should keep the “if and only” wording, for namespace protection and consistency.

- Jim Thomas
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