This gnulib patch modifies "verify" to use C1X's _Static_assert if
running GCC 4.6.0 or later, which generates easier-to-read
diagnostics. I haven't pushed this yet because I thought it wouldn't
hurt to get more pairs of eyes to look at it.
diff --git a/ChangeLog b/ChangeLog
index db0800c..3f3141c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2011-04-04 Paul Eggert <egg...@cs.ucla.edu>
+
+ verify: use _Static_assert if available
+ * lib/verify.h (HAVE__STATIC_ASSERT): New macro.
+ (verify_true, verify): Use it if available. This generates better
+ diagnostics with GCC 4.6.0 and later.
+
2011-04-01 Bruno Haible <br...@clisp.org>
wmemchr, wcschr, wcsrchr, wcspbrk, wcsstr: Avoid errors in C++ mode.
diff --git a/lib/verify.h b/lib/verify.h
index 5e91abd..dac9f77 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -20,6 +20,20 @@
#ifndef VERIFY_H
# define VERIFY_H 1
+/* Define HAVE__STATIC_ASSERT to 1 if _Static_assert works as per the
+ C1X draft N1548 section 6.7.10. This is supported by GCC 4.6.0 and
+ later, and its use here generates easier-to-read diagnostics when
+ verify (R) fails.
+
+ For now, use this with a non-GCC compiler only if __STDC_VERSION__
+ is a high value. The value that will be chosen for C1X is not
+ known yet, but guess that it's at least 201104. Eventually whether
+ _Static_assert works should be determined by 'configure'. */
+# if (201104 <= __STDC_VERSION__ \
+ || 4 < __GNUC__ || (__GNUC__ == 4 && 6 <= __GNUC_MINOR__))
+# define HAVE__STATIC_ASSERT 1
+# endif
+
/* Each of these macros verifies that its argument R is nonzero. To
be portable, R should be an integer constant expression. Unlike
assert (R), there is no run-time overhead.
@@ -31,7 +45,12 @@
Symbols ending in "__" are private to this header.
- The code below uses several ideas.
+ If _Static_assert works, verify (R) uses it directly. Similarly,
+ verify_true (R) works by packaging a _Static_assert inside a struct
+ that is an operand of sizeof.
+
+ The code below uses several ideas for C++ compilers, and for C
+ compilers that do not support _Static_assert:
* The first step is ((R) ? 1 : -1). Given an expression R, of
integral or boolean or floating-point type, this yields an
@@ -109,15 +128,9 @@
__COUNTER__ macro that can let us generate unique identifiers for
each dummy function, to suppress this warning.
- * This implementation exploits the fact that GCC does not warn about
- the last declaration mentioned above. If a future version of GCC
- introduces a warning for this, the problem could be worked around
- by using code specialized to GCC, just as __COUNTER__ is already
- being used if available.
-
- #if 4 <= __GNUC__
- # define verify(R) [another version to keep GCC happy]
- #endif
+ * This implementation exploits the fact that older versions of GCC,
+ which do not support _Static_assert, also do not warn about the
+ last declaration mentioned above.
* In C++, any struct definition inside sizeof is invalid.
Use a template type to work around the problem. */
@@ -148,6 +161,13 @@ template <int w>
struct verify_type__ { unsigned int verify_error_if_negative_size__: w; };
# define verify_true(R) \
(!!sizeof (verify_type__<(R) ? 1 : -1>))
+# elif HAVE__STATIC_ASSERT
+# define verify_true(R) \
+ (!!sizeof \
+ (struct { \
+ _Static_assert (R, "verify_true (" #R ")"); \
+ int verify_dummy__; \
+ }))
# else
# define verify_true(R) \
(!!sizeof \
@@ -157,7 +177,11 @@ template <int w>
/* Verify requirement R at compile-time, as a declaration without a
trailing ';'. */
-# define verify(R) \
+# if HAVE__STATIC_ASSERT
+# define verify(R) _Static_assert (R, "verify (" #R ")")
+# else
+# define verify(R) \
extern int (* _GL_GENSYM (verify_function) (void)) [verify_true (R)]
+# endif
#endif
--
1.7.4
