ISO/IEC JTC1/SC22/WG14 N505

Proposal UK008a - Make qualifiers idempotent
Clive D.W. Feather


Summary
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This proposal allows a type to have more than one occurrence of the same
qualifier; the effect of this is the same as having it only once.


Conformance
-----------
No strictly-conforming application is affected by this proposal. Some
applications which formerly generated a diagnostic become strictly conforming.


Discussion
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C89 allows a type to be qualified only once by a given qualifier. If the
qualifier is hidden in a typedef in a header, it can be almost impossible
to determine whether the type is qualified other than by trial and error.
This proposal allows multiple qualification with no effect. For example,
sig_atomic_t could now be made a volatile type.


Detailed proposal
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In subclause 6.5.3, delete the constraints, and add a new paragraph to
the semantics:

  If the same qualifier appears more than once in the same specifier
  list or qualifier list, either directly or via one or more typedefs,
  the behaviour shall be the same as if it appeared only once.