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Re: [PATCH] assert: Support types without operator== (int) [BZ #21972]
On 08/18/2017 07:40 PM, Florian Weimer wrote:
> On 08/18/2017 07:30 PM, Paul Eggert wrote:
>> 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.
>
> Oh, this works. Updated patch attached.
I think it's still valuable to use static_cast<bool> (expr) for C++
because we don't need any extensions (except __FUNCTION__ for early C++)
because the parentheses do not count in this context; assert (a = 1)
still results in a warning.
Another patch attached.
Thanks,
Florian
assert: Support types without operator== (int) [BZ #21972]
2017-08-18 Florian Weimer <fweimer@redhat.com>
[BZ #21972]
* assert/assert.h (assert): Use static_cast (bool) for C++.
Use the ternary operator in the warning branch for GNU C.
* 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.
diff --git a/assert/Makefile b/assert/Makefile
index 1c3be9b01f..9ec1be81a9 100644
--- a/assert/Makefile
+++ b/assert/Makefile
@@ -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
diff --git a/assert/assert.h b/assert/assert.h
index 6801cfeb10..640c95c063 100644
--- a/assert/assert.h
+++ b/assert/assert.h
@@ -85,7 +85,12 @@ __END_DECLS
/* When possible, define assert so that it does not add extra
parentheses around EXPR. Otherwise, those added parentheses would
suppress warnings we'd expect to be detected by gcc's -Wparentheses. */
-# if !defined __GNUC__ || defined __STRICT_ANSI__
+# if defined __cplusplus
+# define assert(expr) \
+ (static_cast <bool> (expr) \
+ ? void (0) \
+ : __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))
+# elif !defined __GNUC__ || defined __STRICT_ANSI__
# define assert(expr) \
((expr) \
? __ASSERT_VOID_CAST (0) \
@@ -93,12 +98,11 @@ __END_DECLS
# else
/* The first occurrence of EXPR is not evaluated due to the sizeof,
but will trigger any pedantic warnings masked by the __extension__
- for the second occurrence. The explicit comparison against zero is
- required to support function pointers and bit fields in this
- context, and to suppress the evaluation of variable length
- arrays. */
+ for the second occurrence. The ternary operator is required to
+ support function pointers and bit fields in this context, and to
+ suppress the evaluation of variable length arrays. */
# define assert(expr) \
- ((void) sizeof ((expr) == 0), __extension__ ({ \
+ ((void) sizeof ((expr) ? 1 : 0), __extension__ ({ \
if (expr) \
; /* empty */ \
else \
diff --git a/assert/tst-assert-c++.cc b/assert/tst-assert-c++.cc
new file mode 100644
index 0000000000..c001bfff49
--- /dev/null
+++ b/assert/tst-assert-c++.cc
@@ -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>
diff --git a/assert/tst-assert-g++.cc b/assert/tst-assert-g++.cc
new file mode 100644
index 0000000000..8c06402825
--- /dev/null
+++ b/assert/tst-assert-g++.cc
@@ -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>