Issue 0124: What is the difference between casts to a void type versus casts to the void type?

This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.

Authors: Ron Guilmette, WG14
Date: 1993-12-03
Submitted against: C90
Status: Fixed
Fixed in: C90 TC2
Converted from: dr.htm, dr_124.html

ANSI/ISO C Defect Report #rfg31:

Subject: Casts to “a void type” versus casts to “the void type.”

Must a conforming implementation issue a diagnostic for the following code?

void example ()
        {
        (const volatile void) 0;        /* diagnostic required? */
        }

Background:

Subclause 6.3.4 (Constraints):

Unless the type name specifies void type, the type name shall specify qualified or unqualified scalar type and the operand shall have scalar type.

Note that this constraint is not specific about whether a qualified void type is permitted in a cast or not; i.e. it should say either “a void type” or else say “the void type.”

A quick check of several existing implementations seems to indicate that a majority of implementors have assumed that any void type (however qualified) is acceptable in a cast. Therefore it would seem prudent for the Committee to clarify the above quoted rule by changing “void type” to “a void type.”

Comment from WG14 on 1997-09-23:

Correction

In subclause 6.3.4, page 45, change the paragraph under Constraints:

Unless the type name specifies void type, the type name shall specify qualified or unqualified scalar type and the operand shall have scalar type.

to:

Unless the type name specifies a void type, the type name shall specify qualified or unqualified scalar type and the operand shall have scalar type.