Defect Report #102

Submission Date: 03 Dec 93
Submittor: WG14
Source: Ron Guilmette
Question
ANSI/ISO C Defect report #rfg9:
Subclause 6.5 Constraints says:
If an identifier has no linkage, there shall be no more than one declaration of the identifier (in a declarator or type specifier) with the same scope and in the same name space, except for tags as specified in 6.5.2.3.
Subclause 6.5.2.3, Semantics section says:
Subsequent declarations [of a tag] in the same scope shall omit the bracketed list.
Given that one of the above two rules appears in a Constraints section, while the other appears in a Semantics section, it is ambiguous whether or not diagnostics are strictly required in the following cases (in which more than one defining declaration of each tag appears within a single scope):
void example () { struct S { int member; }; struct S { int member; }; /* diagnostic required? */ union U { int member; }; union U { int member; }; /* diagnostic required? */ enum E { member }; enum E { member }; /* diagnostic required? */ }
Response
A diagnostic is required for the struct, union, and enum redeclarations indicated in the question. Subclause 6.5 indicates that there must be a diagnostic ``except for tags as specified in 6.5.2.3.'' In subclause 6.5.2.3, the specified exception is for subsequent declarations that omit the bracketed list.
See also the response to Defect Report #017, Question 3.
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