Issue 0017.08: What types are compatible with pointer to void?

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

Authors: Derek M. Jones, WG14
Date: 1992-12-10
Reference document: X3J11/90-056
Submitted against: C90
Status: Closed
Converted from: dr.htm, dr_017.html

Compatibility of pointer to void with storage class

Refer to subclause 6.3.9, page 49, lines 24-25. Do these lines make the following legal?

register void *p;
 char *q;
 if (p==q)  /* legal */
 ...

The wording on line 25, “... version of void; or” does not talk about the “void type.” This sentence could be taken as simply referring to the occurrence of a qualified or unqualified occurrence of void.

Should the wording on line 25 be changed to “... version of the type void; or” and thus cause the storage class to be ignored, or does the above example fall outside the scope of the constraint?

Comment from WG14 on 1997-09-23:

Response

The relevant citation is subclause 6.3.9:

one operand is a pointer to an object or incomplete type and the other is a pointer to a qualified or unqualified version of void; or

The Committee believes that the current wording of the standard is clear, and it is not changed in meaning by changing “version of void” in the quoted section to “version of the void type.”

The standard uses the word “void” in two contexts: the keyword itself and the type that the keyword names. The context that the word is used in adequately distinguishes between the two. In the section quoted, which discusses type compatibility, a misreading of “void” as meaning the keyword quickly results in nonsense.

As to the qualification discussed in the quoted passage, it is type qualification, defined in subclause 6.5.3. The standard only uses the words “qualified” and “unqualified” when discussing type qualification and never uses them when discussing storage classes. Thus, storage classes have no place in the discussion of the quoted passage.