This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
[Bug c++/54325] New: C++11 uniform initialization syntax for argument-less abstract base class constructor fails
- From: "moritz at bunkus dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Sun, 19 Aug 2012 18:29:00 +0000
- Subject: [Bug c++/54325] New: C++11 uniform initialization syntax for argument-less abstract base class constructor fails
- Auto-submitted: auto-generated
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54325
Bug #: 54325
Summary: C++11 uniform initialization syntax for argument-less
abstract base class constructor fails
Classification: Unclassified
Product: gcc
Version: 4.7.1
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c++
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: moritz@bunkus.org
Using {} syntax for base class initialization fails with "cannot allocate an
object of abstract type 'Base'" for abstract base classes with argument-less
constructors. I'll include two code samples. The first one does work with g++
4.6.1 (Ubuntu 11.10), g++ 4.6.3 (Ubuntu 12.04) and clang 3.1 but does NOT work
with g++ 4.7.0 (Ubuntu 12.04) and g++ 4.7.1 (self-compiled). The second one
works with 4.7.0 and 4.7.1 as well.
Example code that does NOT work with 4.7.x but does with older versions/other
compilers:
class Base {
public:
Base() {};
virtual ~Base() {};
virtual void do_stuff() = 0;
};
class Derived: public Base {
public:
Derived() : Base{} {};
virtual ~Derived() {};
virtual void do_stuff() {};
};
int
main() {
Derived d;
return 0;
}
Changing Base's constructor to take an additional argument lets it work
suddenly:
class Base {
public:
int m_dummy;
Base(int dummy): m_dummy{dummy} {};
virtual ~Base() {};
virtual void do_stuff() = 0;
};
class Derived: public Base {
public:
Derived() : Base{42} {};
virtual ~Derived() {};
virtual void do_stuff() {};
};
int
main() {
Derived d;
return 0;
}
$ ~/opt/gcc/4.7.1/bin/g++ -v
Using built-in specs.
COLLECT_GCC=/home/mosu/opt/gcc/4.7.1/bin/g++
COLLECT_LTO_WRAPPER=/home/mosu/opt/gcc/4.7.1/libexec/gcc/x86_64-unknown-linux-gnu/4.7.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ./configure --enable-checking=release --enable-languages=c,c++
--prefix=/home/mosu/opt/gcc/4.7.1
Thread model: posix
gcc version 4.7.1 (GCC)
Actual error message:
$ ~/opt/gcc/4.7.1/bin/g++ -std=c++11 -o fails fails.cpp
fails.cpp: In constructor âDerived::Derived()â:
fails.cpp:11:20: error: cannot allocate an object of abstract type âBaseâ
fails.cpp:1:7: note: because the following virtual functions are pure within
âBaseâ:
fails.cpp:6:16: note: virtual void Base::do_stuff()