Issue 0017.18: Are f() and f(void) compatible?

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 functions with void and no prototype

f2(void);
 f2(); /* Is this function compatible with the one above? */

Now subclause 6.5.4.3, page 68, line 1 says that the first declaration of f2 specifies that the function has no parameters.

No rules are given in the subsequent paragraphs to say that a function declaration with a parameter type list, with no parameters, is compatible with a function declaration with an empty parameter list.

If we treat the void as a single parameter then page 68, lines 14-18 would make the above two functions incompatible. void is not compatible with any default promotions. subclause 6.5.4.3, page 68, lines 18-22 cover the case for declaration and definition.

Thus I think that in the above example the behavior is implicitly undefined.

Comment from WG14 on 1997-09-23:

Response

Subclause 6.5.4.3, page 67, line 37 and page 68, line 1 state, “The special case of void as the only item in the list specifies that the function has no parameters.” Therefore, in the case of f2(void); there are no parameters just as there are none for f2();. Since both functions have the same return type, these declarations are compatible.