http://llvm.org/bugs/show_bug.cgi?id=6345
Summary: [GNU Extension] Clang differs from GCC on anonymous
structs
Product: clang
Version: trunk
Platform: PC
OS/Version: All
Status: NEW
Severity: normal
Priority: P2
Component: Semantic Analyzer
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Consider the following:
union foo {
struct {
union {
struct {void* bar[4];};
} u;
struct {
union {int baz;} u;
};
} s;
};
int f(void) {
union foo foo;
foo.s.u.bar[2] = (void*)0;
foo.s.u.baz = 0;
}
When GCC 4.2 is run on this example, it produces the following:
foo.c: In function âfâ:
foo.c:17: error: âunion <anonymous>â has no member named âbazâ
but when Clang is run on the example, it produces this:
test-su.c:7:23: error: member of anonymous struct redeclares 'u'
union { int baz; } u;
^
test-su.c:5:5: note: previous declaration is here
} u;
^
test-su.c:16:10: error: no member named 'bar' in 'union foo::<anonymous>'; did
you mean 'baz'?
foo.s.u.bar[2] = (void*)0;
^~~
baz
test-su.c:7:16: note: 'baz' declared here
union { int baz; } u;
^
test-su.c:16:13: error: subscripted value is not an array, pointer, or vector
foo.s.u.bar[2] = (void*)0;
~~~~~~~~~~~^~
5 diagnostics generated.
It does not matter if Clang is in C99 or C89 mode (with GNU extensions, of
course).
So there's two differences between clang and GCC:
- Clang complains if a member is redeclared in an anonymous struct. GCC simply
discards the second declaration.
- Interestingly, clang then hides the first definition, using only the second
one. GCC simply discards the second one.
I don't know if you want to fix this, but the union construct has appeared in
the wild, specifically in Wine, and they're loath to change it. After all, it's
worked well for them for the past 10 years with GCC.
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