While working on a policy-based smart pointer I discovered that copy-initialization, base-from-derived, using Colvin-Gibbons trick, does not work for std::auto ptr with gcc. It also reproduces with OpenSUSE 11.0 with gcc 4.3.1 (now I am on 10.3 with gcc 4.2.1).
The technique and test is described in Fixing auto_ptr: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/1997/N1128.pdf The options given when GCC was configured/built: gcc -v Using built-in specs. Target: i586-suse-linux Configured with: ../configure --enable-threads=posix --prefix=/usr --with-local-prefix=/usr/local --infodir=/usr/share/info --mandir=/usr/share/man --libdir=/usr/lib --libexecdir=/usr/lib --enable-languages=c,c++,objc,fortran,obj-c++,java,ada --enable-checking=release --with-gxx-include-dir=/usr/include/c++/4.2.1 --enable-ssp --disable-libssp --disable-libgcj --with-slibdir=/lib --with-system-zlib --enable-shared --enable-__cxa_atexit --enable-libstdcxx-allocator=new --disable-libstdcxx-pch --program-suffix=-4.2 --enable-version-specific-runtime-libs --without-system-libunwind --with-cpu=generic --host=i586-suse-linux Thread model: posix gcc version 4.2.1 (SUSE Linux) The complete command line that triggers the bug (from KDevelop output): g++ -DHAVE_CONFIG_H -I. -I.. -I/home/cristia/Work/test_auto_ptr_colvin_gibbons/src -O0 -g3 -MT test_auto_ptr_colvin_gibbons.o -MD -MP -MF .deps/test_auto_ptr_colvin_gibbons.Tpo -c -o test_auto_ptr_colvin_gibbons.o /home/cristia/Work/test_auto_ptr_colvin_gibbons/src/test_auto_ptr_colvin_gibbons.cpp The compiler output: /home/cristia/Work/test_auto_ptr_colvin_gibbons/src/test_auto_ptr_colvin_gibbons.cpp: In function 'int main(int, char**)': /home/cristia/Work/test_auto_ptr_colvin_gibbons/src/test_auto_ptr_colvin_gibbons.cpp:72: error: no matching function for call to 'std::auto_ptr<Base>::auto_ptr(std::auto_ptr<Base>)' /usr/include/c++/4.2.1/memory:349: note: candidates are: std::auto_ptr<_Tp>::auto_ptr(std::auto_ptr_ref<_Tp>) [with _Tp = Base] /usr/include/c++/4.2.1/memory:212: note: std::auto_ptr<_Tp>::auto_ptr(std::auto_ptr<_Tp1>&) [with _Tp1 = Base, _Tp = Base] /usr/include/c++/4.2.1/memory:199: note: std::auto_ptr<_Tp>::auto_ptr(std::auto_ptr<_Tp>&) [with _Tp = Base] /home/cristia/Work/test_auto_ptr_colvin_gibbons/src/test_auto_ptr_colvin_gibbons.cpp:72: error: initializing argument 1 of 'void UseBase(AutoPtrBase)' from result of 'std::auto_ptr<_Tp>::operator std::auto_ptr<_Tp1>() [with _Tp1 = Base, _Tp = Derived]' gmake[2]: *** [test_auto_ptr_colvin_gibbons.o] Error 1 gmake[2]: Target `all' not remade because of errors. gmake[2]: Nothing to be done for `all-am'. gmake[1]: *** [all-recursive] Error 1 gmake: *** [all] Error 2 *** Exited with status: 2 *** Test program: #include <memory> class Base { public: virtual ~Base() {} virtual void Hello() {} }; class Derived: public Base { public: virtual void Hello() {} }; typedef std::auto_ptr<int> AutoPtrInt; typedef std::auto_ptr<Base> AutoPtrBase; typedef std::auto_ptr<Derived> AutoPtrDerived; AutoPtrInt CreateInt() { return AutoPtrInt(new int); } void UseInt(AutoPtrInt ptr) { (*ptr)++; }; AutoPtrDerived CreateDerived() { return AutoPtrDerived(new Derived); } void UseBase(AutoPtrBase ptr) { ptr->Hello(); } int main(int argc, char *argv[]) { { AutoPtrInt api(CreateInt()); // 1. Direct-initialization, same type: OK } { UseInt(CreateInt()); // 2. Copy-initialization, same type: OK } { AutoPtrBase apb(CreateDerived()); // 3. Direct-initialization, base-from-derived: OK } { // 4. Copy-initialization, base-from-derived: Does not compile!!! UseBase(CreateDerived()); // Quick workaround UseBase(AutoPtrBase(CreateDerived())); } return 0; } Thanks, Cristian -- Summary: std::auto_prtr copy-initialization, base-from-derived (Colvin-Gibbons trick) does not work Product: gcc Version: 4.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: cristian_anita at yahoo dot com GCC build triplet: i586-suse-linux GCC host triplet: i586-suse-linux GCC target triplet: i586-suse-linux http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37255