https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66632
Bug ID: 66632
Summary: Incorrect use of default constructor to initialize
isolated rvalue.
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jasonxbell at gmail dot com
Target Milestone: ---
Created attachment 35828
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35828&action=edit
Preprocessed source file
In the following code, the first statement in main() -- 'Q(S1v1)' -- creates an
isolated rvalue; g++ uses the default constructor to initialize it instead of
'Q::Q(S1 x)'. The lvalue q1 is then init'd via copy of the (incorrectly init'd)
rvalue from the previous statement.
bug2.c:
--------------------------------------------------------------------------------
#include <iostream>
using std::cout;
using std::ostream;
enum S1 { S1v0 = 0, S1v1= 10, S1v2, S1v3 };
class Q
{
public:
Q() : mySN(nextSN++), s1val(S1v0) { cout << "+Q
#" << mySN << " Default\n"; }
Q(const Q &src ) : mySN(nextSN++), s1val(src.s1val) { cout << "+Q
#" << mySN << " Copy from #" << src.mySN << '\n'; }
explicit Q(S1 x) : mySN(nextSN++), s1val(x) { cout << "+Q
#" << mySN << " from S1\n"; }
private:
int mySN;
S1 s1val;
static int nextSN;
friend ostream& operator<<( ostream &out, const Q &obj );
};
int Q::nextSN = 1;
ostream& operator<<( ostream &out, const Q &obj )
{
out << "Q #" << obj.mySN << " == " << obj.s1val << '\n';
return out;
}
int main( void )
{
Q(S1v1);
Q q2{S1v1};
cout << '\n';
cout << q2;
return 0;
}
--------------------------------------------------------------------------------
Compile and run:
$ g++ -std=c++11 -pedantic -Wall -Wextra bug2.cpp; ./a.exe
+Q #1 Default
+Q #2 Copy from #1
Q #2 == 0
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-cygwin/4.9.2/lto-wrapper.exe
Target: x86_64-pc-cygwin
Configured with:
/cygdrive/i/szsz/tmpp/gcc/gcc-4.9.2-3.x86_64/src/gcc-4.9.2/configure
--srcdir=/cygdrive/i/szsz/tmpp/gcc/gcc-4.9.2-3.x86_64/src/gcc-4.9.2
--prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin
--libexecdir=/usr/libexec --datadir=/usr/share --localstatedir=/var
--sysconfdir=/etc --libdir=/usr/lib --datarootdir=/usr/share
--docdir=/usr/share/doc/gcc --htmldir=/usr/share/doc/gcc/html -C
--build=x86_64-pc-cygwin --host=x86_64-pc-cygwin --target=x86_64-pc-cygwin
--without-libiconv-prefix --without-libintl-prefix --libexecdir=/usr/lib
--enable-shared --enable-shared-libgcc --enable-static
--enable-version-specific-runtime-libs --enable-bootstrap --enable-__cxa_atexit
--with-dwarf2 --with-tune=generic
--enable-languages=ada,c,c++,fortran,lto,objc,obj-c++ --enable-graphite
--enable-threads=posix --enable-libatomic --enable-libgomp --disable-libitm
--enable-libquadmath --enable-libquadmath-support --enable-libssp
--enable-libada --enable-libgcj-sublibs --disable-java-awt --disable-symvers
--with-ecj-jar=/usr/share/java/ecj.jar --with-gnu-ld --with-gnu-as
--with-cloog-include=/usr/include/cloog-isl --without-libiconv-prefix
--without-libintl-prefix --with-system-zlib --enable-linker-build-id
Thread model: posix
gcc version 4.9.2 (GCC)
