http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52796
Bug #: 52796 Summary: [4.6/4.7 C++11] Initialization of primitive object with 0-length parameter pack fails to value-initialize Classification: Unclassified Product: gcc Version: 4.7.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassig...@gcc.gnu.org ReportedBy: jyass...@gcc.gnu.org The following program attempts to initialize a 'char' member using a variadic parameter pack. With length 0, the initialization doesn't happen, leaving the original value of the memory in the field. I originally noticed this in gcc-4.6 when std::list<char>(3) failed to initialize the list elements. $ cat test.cc #include <memory.h> #include <iostream> template<typename T> class Wrapper { public: #if WORK Wrapper() : t() { } #endif template<typename ...Args> Wrapper(Args&&... args) : t(args...) { } T t; }; int main() { __attribute__(aligned(alignof(Wrapper<char>))) char space[sizeof(Wrapper<char>)]; memset(space, '\xab', sizeof(space)); Wrapper<char>*w = new(space) Wrapper<char>; std::cout << (int)w->t << '\n'; w->~Wrapper<char>(); memset(space, '\xab', sizeof(space)); w = new(space) Wrapper<char>(); std::cout << (int)w->t << '\n'; w->~Wrapper<char>(); memset(space, '\xab', sizeof(space)); w = new(space) Wrapper<char>((int)'y'); std::cout << (int)w->t << '\n'; w->~Wrapper<char>(); } $ g++-4.7pre --version g++-4.7pre (GCC) 4.7.1 20120330 (prerelease) ... $ g++-4.7pre -Wall -std=c++11 test.cc -g3 -o test && ./test -85 0 121 Disassembling with gdb shows: Dump of assembler code for function Wrapper<char>::Wrapper<>(): 0x0000000000400a70 <+0>: push %rbp 0x0000000000400a71 <+1>: mov %rsp,%rbp 0x0000000000400a74 <+4>: mov %rdi,-0x8(%rbp) => 0x0000000000400a78 <+8>: pop %rbp 0x0000000000400a79 <+9>: retq