Building a testdir of module 'assert-h' with CC="gcc" CXX="g++ -std=gnu++11"
on CentOS 7, I get a compilation error:
g++ -std=gnu++11 -DHAVE_CONFIG_H -I. -I.. -DGNULIB_STRICT_CHECKING=1
-DIN_GNULIB_TESTS=1 -I. -I. -I.. -I./.. -I../gllib -I./../gllib -Wno-error -g
-O2 -MT test-assert-h-c++.o -MD -MP -MF .deps/test-assert-h-c++.Tpo -c -o
test-assert-h-c++.o test-assert-h-c++.cc
In file included from ../config.h:716:0,
from test-assert-h-c++.cc:20:
/usr/include/c++/4.8.2/type_traits:934:7: error: storage class specified for
‘_gl_static_assert_function2’
static_assert(sizeof...(_Args) > 1,
^
make[4]: *** [test-assert-h-c++.o] Error 1
The situation with this compiler ("g++ -std=gnu++11") is:
- It supports 2-args static_assert in version >= 4.7,
- It supports 1-arg static_assert in version >= 6,
- It never supports _Static_assert.
Thus the fix (for the versions >= 4.7, < 6) is to redefine
'static_assert', but like via _GL_VERIFY (which cannot appear
inside struct {...} or class {...}), but via a macro that
dispatches on the number of arguments. Similar to what we did
for MSVC 14, just with the difference that here we can assume
an ISO C compatible preprocessor.
For completeness, I tested also "clang++ -std=gnu++11"). Here,
there is no problem: It supports 2-args static_assert and
1-arg static_assert at least in versions >= 4. It emits a warning
warning: static_assert with no message is a C++1z extension
[-Wc++1z-extensions]
in the 1-arg case, which (AFAIU) is correct.
2024-05-30 Bruno Haible <br...@clisp.org>
assert-h, verify: Fix compilation error with g++ (4.8.5) -std=gnu++11.
Reported by Harmen <har...@stoppels.ch> at
<https://savannah.gnu.org/bugs/index.php?65811>.
* lib/verify.h (static_assert): In C++ mode with g++ < 6 and
-std=gnu++11, define in a way that supports also the 1-argument
invocations and the invocations inside C++ struct and class.
diff --git a/lib/verify.h b/lib/verify.h
index 08268c2498..978926a491 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -259,11 +259,22 @@ template <int w>
&& (!defined __cplusplus \
|| (__cpp_static_assert < 201411 \
&& __GNUG__ < 6 && __clang_major__ < 6 && _MSC_VER < 1910)))
-# if defined __cplusplus && _MSC_VER >= 1900 && !defined __clang__
+# if (defined __cplusplus && defined __GNUG__ && __GNUG__ < 6 \
+ && __cplusplus == 201103L && !defined __clang__)
+/* g++ >= 4.7, < 6 with option -std=c++11 or -std=gnu++11 supports the
+ two-arguments static_assert but not the one-argument static_assert, and
+ it does not support _Static_assert.
+ We have to play preprocessor tricks to distinguish the two cases. */
+# define _GL_SA1(a1) static_assert ((a1), "static assertion failed")
+# define _GL_SA2 static_assert
+# define _GL_SA3 static_assert
+# define _GL_SA_PICK(x1,x2,x3,x4,...) x4
+# define static_assert(...) _GL_SA_PICK(__VA_ARGS__,_GL_SA3,_GL_SA2,_GL_SA1)
(__VA_ARGS__)
+# elif defined __cplusplus && _MSC_VER >= 1900 && !defined __clang__
/* MSVC 14 in C++ mode supports the two-arguments static_assert but not
the one-argument static_assert, and it does not support _Static_assert.
We have to play preprocessor tricks to distinguish the two cases.
- Since the MSVC preprocessor is not ISO C compliant (see above),.
+ Since the MSVC preprocessor is not ISO C compliant (see above),
the solution is specific to MSVC. */
# define _GL_EXPAND(x) x
# define _GL_SA1(a1) static_assert ((a1), "static assertion failed")
