[PATCH] test-stddef: test offsetof compliance

[Eric Blake]

* tests/test-stddef.c: Add tests for offsetof.

Signed-off-by: Eric Blake <address@hidden>
---

I was about to push this, so we can detect any gotchas with using
offsetof according to POSIX.  Then I decided to test first.

And the first loser is Solaris' /usr/bin/cc:
"../../gltests/test-stddef.c", line 44: syntax error before or at: &
"../../gltests/test-stddef.c", line 44: warning: syntax requires ";" after last 
struct/union member
"../../gltests/test-stddef.c", line 44: zero-sized struct/union
"../../gltests/test-stddef.c", line 44: cannot recover from previous errors
cc: acomp failed for ../../gltests/test-stddef.c

Adding "redundant" parens to the sizeof(offsetof()) call fixed the
it for that compiler.  Sure enough, /usr/include/iso/stddef_iso.h has:

#define offsetof(s, m)  (std::size_t)(&(((s *)0)->m))

So before I push, I guess we need to beef up the stddef module
to detect and work around broken compilers/headers that don't
properly parenthesize their offsetof macro.

 ChangeLog           |    5 +++++
 tests/test-stddef.c |   10 ++++++++++
 2 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 86de94d..896557a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2010-08-16  Eric Blake  <address@hidden>
+
+       test-stddef: test offsetof compliance
+       * tests/test-stddef.c: Add tests for offsetof.
+
 2010-08-15  Bruno Haible  <address@hidden>

        stpncpy: Allow stpncpy to be defined as a macro.
diff --git a/tests/test-stddef.c b/tests/test-stddef.c
index d047e57..be8bc5e 100644
--- a/tests/test-stddef.c
+++ b/tests/test-stddef.c
@@ -31,6 +31,16 @@ size_t c = 2;
    per POSIX 2008.  */
 verify (sizeof NULL == sizeof (void *));

+/* Check that offsetof produces integer constants with correct type.  */
+struct d
+{
+  char e;
+  char f;
+};
+verify (sizeof offsetof (struct d, e) == sizeof (size_t));
+verify (offsetof (struct d, e) < -1); /* Must be unsigned.  */
+verify (offsetof (struct d, f) == 1);
+
 int
 main (void)
 {
-- 
1.7.2.1