Defect Report #105
Submission Date: 03 Dec 93
Source: Ron Guilmette
ANSI/ISO C Defect report #rfg12:
Subclause 6.5 says (in its Constraints section):
All declarations in the same scope that refer to the same object
or function shall specify compatible types.
However in subclause 18.104.22.168 we have the following rule:
All declarations that refer to the same object or function shall
have compatible type; otherwise the behavior is undefined.
There is a conflict between the meaning of these two rules. The former
rule indicates declaring something in two or more incompatible ways
(in a given scope) must cause a diagnostic, while the latter
rule indicates that doing the exact same thing may result in undefined
behavior (i.e. possibly silent acceptance of the code by the implementation).
(Note that this same issue was raised previously in the C Information
Bulletin #1, RFI #17, question #3.
While the response to that question indicated that no change was needed, a
change is clearly need in order to resolve this ambiguity.)
Furthermore, the use of the term ``refer to'' in both of these
rules seems both unnecessary and potentially confusing. Why not just
talk instead about declarations ``declaring'' things, rather
than ``referring to'' those things?
To eliminate the first problem I would suggest that the rules quoted
above from subclause 22.214.171.124 should be clarified as follows:
If any pair of declarations of the same object or function which
appear in different scopes declare the object or function in question
to have two different incompatible types, the behavior is undefined.
(Actually the rule regarding declaration compatability which now appears
in subclause 126.96.36.199 seems entirely misplaced anyway. Shouldn't it
just be taken out of subclause 188.8.131.52 and moved to the subclause
on declarations, i.e. subclause 6.5?)
This error was corrected in response to Defect Report #017, Question 3.
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