Defect Report #105

Submission Date: 03 Dec 93
Submittor: WG14
Source: Ron Guilmette
Question
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 6.1.2.6 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 6.1.2.6 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 6.1.2.6 seems entirely misplaced anyway. Shouldn't it just be taken out of subclause 6.1.2.6 and moved to the subclause on declarations, i.e. subclause 6.5?)
Response
This error was corrected in response to Defect Report #017, Question 3.
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