Defect Report #113

Submission Date: 03 Dec 93
Submittor: WG14
Source: Ron Guilmette
Question
ANSI/ISO C Defect report #rfg20:
Subject: Return expressions in functions declared to return qualified void.
a) Does the following code involve usage which requires a diagnostic from a conforming implementation?
b) Does the following code involve usage which renders the code itself not strictly conforming?
volatile void func0 (volatile void *vvp)
{
return *vvp; /* ? */
}

const void func1 (const void *cvp)
{
return *cvp; /* ? */
}
Background:
Subclause 6.6.6.4 (Constraints):
A return statement with an expression shall not appear in a function whose return type is void.
Note that this constraint doesn't say anything about functions declared to return some qualified version of the void type.
I believe that it was probably the Committee's true intent to require a diagnostic for any attempt to specify an expression in a return statement within any function declared to return any qualified or unqualified version of the void type (and indeed, many existing implementations do already issue diagnostics for usage such as that shown in the example above). Thus, it would seem appropriate for the Committee to amend the above quoted constraint (from subclause 6.6.6.4) to read:
A return statement with an expression shall not appear in a function whose return type is a void type.
Response
a) Yes, a diagnostic is required.
b) Yes, this renders the program not strictly conforming code.
A qualified void function return type is disallowed by the constraints of subclause 6.7.1:
The return type from a function shall be void or an object type other than array.
The constraint does not say ``a void type'' and thus void must not be qualified when used as a function return type. Since a qualified void return type is already invalid, there is no need for the additional constraint on the return statement (subclause 6.6.6.4).
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