Defect Report #169

Submis>sion 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 017: Trigraphs
The C Standard's description of the replacement of trigraphs is contradictory.
Subclause reads in part:
All occurrences in a source file of the following sequences of three characters (called trigraph sequences [7]) are replaced with the corresponding single character... Each ? that does not begin one of the trigraphs listed above is not changed.
Since the second character in each trigraph is a ? that does not begin the trigraph, this is a direct contradiction.
Suggested Technical Corrigendum
Change the last sentence of the cited text to:
Each ? that is not part of one of the trigraphs listed above is not changed.
Proposed Response
The C Standard is clear enough as is. A trigraph begins with two question marks, so it is reasonable to refer to both of them as beginning the trigraph.
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