This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.
Authors: Sam Kendall, WG14
Date: 1992-12-10
Reference document: X3J11/90-047
Submitted against: C90
Status: Closed
Converted from: dr.htm, dr_013.html
“Compatible” not defined for recursive types
The term “compatible” is not completely defined. Consider the following two file-scope declarations in separate translation units:
extern struct a { struct a *p; } x;
struct a { struct a *p; } x;
Are these two declarations of x compatible? Obviously they should be, but
subclause 6.1.2.6 does not say so.
Because subclause 6.1.2.6 does not say how to terminate the recursion in testing for compatibility of two recursive types, either interpretation is possible. In other words, it is consistent with the rules in subclause 6.1.2.6 to decide that the two declarations are compatible; but it is also consistent to decide that they are incompatible.
We can solve the problem roughly as follows: append the following draft sentence to the first paragraph of subclause 6.1.2.6 (page 25, line 8):
If two types declared in separate translation units admit the possibility of being either compatible or incompatible, the two types shall be compatible.* [Footnote *: This case occurs with recursive types.]
This sentence is not satisfactory; perhaps another Committee member can state this rule better.
Comment from WG14 on 1997-09-23:
We agree that the C Standard can be read in a way that it “loops.” Our intent, and we feel the only reasonable solution, is that the recursion stops and the two types are regarded as compatible.