Defect Report #176

Submission Date: 16 Oct 95
Submittor: BSI
Source: Clive D.W. Feather
Submitted to BSI by Clive D.W. Feather .
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 024: Diagnostics for #error
The rules concerning whether #error generates a diagnostic are contradictory.
Subclause reads:
A conforming implementation shall produce at least one diagnostic message (identified in an implementation-defined manner) for every translation unit that contains a violation of any syntax rule or constraint. Diagnostic messages need not be produced in other circumstances.

Subclause 6.8.5 reads:
A preprocessing directive of the form
# error pp-tokens new-line opt

causes the implementation to produce a diagnostic message that includes the specified sequence of preprocessing tokens.
Since this is not in a Constraints section, these two statements directly contradict one another. Furthermore, the second statement can be read as applying to a #error directive that is excluded by a false #if condition.
Suggested Technical Corrigendum
In subclause 6.8.5, replace the entire subclause with:
A #error preprocessing directive shall not occur in a translation unit. Any diagnostic message generated because of the violation of this constraint [Footnote: The intent of this subclause is that #error indicates that translation should fail. As stated in subclause, a translation unit excludes lines within the false side of #if ... #else ... #endif groups.] shall include the sequence of preprocessing tokens in the directive.
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