assert: Support types without operator== (int) [BZ #21972]
Commit Message
2017-08-18 Florian Weimer <fweimer@redhat.com>
[BZ #21972]
* assert/assert.h (assert): Use static_cast (bool) for C++ in the
pedantic warning check, to avoid a requirement for operator== (int).
* assert/Makefile (tests): Add tst-assert-c++, tst-assert-g++.
(CFLAGS-tst-assert-c++.o): Compile in C++11 mode.
(CFLAGS-tst-assert-g++.o): Compile in GnU C++11 mode.
(LDLIBS-tst-assert-c++, LDLIBS-tst-assert-g++): Link with libstdc++.
* assert/tst-assert-c++.cc, assert/tst-assert-g++.cc: New files.
Comments
Florian Weimer wrote:
> + ((void) sizeof (static_cast<bool> (expr)), __extension__ ({ \
Can we instead replace 'sizeof ((expr) == 0)' with 'sizeof !(expr)'? That works
in C, and if it also works in C++ it would avoid the need for the #ifdef
__cplusplus.
* Paul Eggert:
> Florian Weimer wrote:
>> + ((void) sizeof (static_cast<bool> (expr)), __extension__ ({ \
>
> Can we instead replace 'sizeof ((expr) == 0)' with 'sizeof !(expr)'?
> That works in C, and if it also works in C++ it would avoid the need
> for the #ifdef __cplusplus.
It does not work in C++ because operator! could have been overloaded
or deleted. It is likely that a future C++ standard will only require
that the expression can be contextually converted to bool, and this is
what the static_cast approach relies upon.
Florian Weimer wrote:
>> Florian Weimer wrote:
>>> + ((void) sizeof (static_cast<bool> (expr)), __extension__ ({ \
>> Can we instead replace 'sizeof ((expr) == 0)' with 'sizeof !(expr)'?
>> That works in C, and if it also works in C++ it would avoid the need
>> for the #ifdef __cplusplus.
> It does not work in C++ because operator! could have been overloaded
> or deleted.
OK, then how about 'sizeof ((expr) ? 1 : 0)'? This should work because ?: cannot
be overloaded.
@@ -25,6 +25,15 @@ include ../Makeconfig
headers := assert.h
routines := assert assert-perr __assert
-tests := test-assert test-assert-perr
+tests := test-assert test-assert-perr tst-assert-c++ tst-assert-g++
include ../Rules
+
+ifeq ($(have-cxx-thread_local),yes)
+CFLAGS-tst-assert-c++.o = -std=c++11
+LDLIBS-tst-assert-c++ = -lstdc++
+CFLAGS-tst-assert-g++.o = -std=gnu++11
+LDLIBS-tst-assert-g++ = -lstdc++
+else
+tests-unsupported += tst-assert-c++ tst-assert-g++
+endif
@@ -97,13 +97,25 @@ __END_DECLS
required to support function pointers and bit fields in this
context, and to suppress the evaluation of variable length
arrays. */
-# define assert(expr) \
+# ifndef __cplusplus
+# define assert(expr) \
((void) sizeof ((expr) == 0), __extension__ ({ \
if (expr) \
; /* empty */ \
else \
__assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION); \
}))
+# else /* __cplusplus */
+/* If EXPR is a type without a matching operrator== (int), the C
+ definition above does not work. */
+# define assert(expr) \
+ ((void) sizeof (static_cast<bool> (expr)), __extension__ ({ \
+ if (expr) \
+ ; /* empty */ \
+ else \
+ __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION); \
+ }))
+# endif
# endif
# ifdef __USE_GNU
new file mode 100644
@@ -0,0 +1,72 @@
+/* Tests for interactions between C++ and assert.
+ Copyright (C) 2017 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <assert.h>
+
+/* The C++ standard requires that if the assert argument is a constant
+ subexpression, then the assert itself is one, too. */
+constexpr int
+check_constexpr ()
+{
+ return (assert (true), 1);
+}
+
+/* Objects of this class can be contextually converted to bool, but
+ cannot be compared to int. */
+struct no_int
+{
+ no_int () = default;
+ no_int (const no_int &) = delete;
+
+ explicit operator bool () const
+ {
+ return true;
+ }
+};
+
+/* This class tests that operator== is not used by assert. */
+struct bool_and_int
+{
+ bool_and_int () = default;
+ bool_and_int (const no_int &) = delete;
+
+ explicit operator bool () const
+ {
+ return true;
+ }
+
+ template <class T> bool operator== (T) const; /* No definition. */
+};
+
+static int
+do_test ()
+{
+ {
+ no_int value;
+ assert (value);
+ }
+
+ {
+ bool_and_int value;
+ assert (value);
+ }
+
+ return 0;
+}
+
+#include <support/test-driver.c>
new file mode 100644
@@ -0,0 +1,19 @@
+/* Tests for interactions between C++ and assert. GNU C++11 version.
+ Copyright (C) 2017 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <tst-assert-c++.cc>