Defect Report #160

Submission Date: 16 Oct 95
Submittor: BSI
Source: Clive D.W. Feather
Question
Submitted to BSI by Clive D.W. Feather [email protected] .
In this Defect Report, identifiers lexically identical to those declared in standard headers refer to the identifiers declared in those standard headers, whether or not the header is explicitly mentioned.
This Defect Report has been prepared with considerable help from Mark Brader, Jutta Degener, Ronald Guilmette, and a person whose employment conditions require anonymity. However, except where stated, opinions expressed or implied should not be assumed to be those of any person other than myself.
Defect Report UK 008: Reservation of identifiers
The C Standard is unclear in its description of what applications can and cannot do with identifiers that are reserved to the implementation for certain uses.
Subclause 7.1.3 reads in part:
Each identifier with file scope listed in any of the following subclauses (including the future library directions) is reserved for use as an identifier with file scope in the same name space if any of its associated headers is included.
Does this include reservation as macros? In particular, is the following code:
#include <stddef.h > #define size_t 42 strictly conforming, or could it cause a redefinition of the macro size_t? Similarly, can another macro legitimately defined by stddef.h (such as offsetof) include size_t in its replacement list, so that:
#include <stddef.h > #undef size_t #define size_t 42 /* ... */ offsetof (struct_type, field) fails to expand correctly? It is not clear how the wording of Footnote 91 applies, and this is in any case not part of the C Standard (except in Australia :-).
Suggested Future Change
In subclause 7.1.3, Reserved Identifiers, change bullet 2 to:

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

Change bullet 5 to:

Each identifier with file scope listed in any of the following subclauses (including the Future library directions) is reserved for use as a macro and as an identifier with file scope in the same name space if any of its associated headers is included.

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