Vector reallocation uses copy instead of move cons

Question

Hi I created a class Foo with a noexcept move constructor using gcc 4.7 and set the vector reserve size to 2 so that it would have to reallocate the size when adding the 3rd item. It seems it is calling the copy constructor instead of the move constructor when doing this. Am I missing something here?

#include <vector>
#include <iostream>

class Foo
{
  public:
  Foo(int x) : data_(x)
  {
    std::cout << " constructing " << std::endl;
  }

  ~Foo()
  {
    std::cout << " destructing " << std::endl;
  }

  Foo& operator=(const Foo&) = default;
  Foo& operator=(Foo&&) = default;

   Foo(Foo&& other) noexcept : data_(std::move(other.data_))
   {
    std::cout << " Move constructing " << std::endl;
   }

   Foo(const Foo& other) noexcept :  data_(other.data_)
   {
    std::cout << " Copy constructing " << std::endl;
   }

  private:
  int data_;
};


int main ( int argc, char *argv[])
{
  std::vector<Foo> v;
  v.reserve(2);
  v.emplace_back(1);
  std::cout << "Added 1" << std::endl;
  v.emplace_back(2);
  std::cout << "Added 2" << std::endl;
  v.emplace_back(3);
  std::cout << "Added 3" << std::endl;
  std::cout << "v size: " << v.size() << std::endl;
}

output:

 constructing 
Added 1
 constructing 
Added 2
 constructing 
 Copy constructing 
 Copy constructing 
 destructing 
 destructing 
Added 3
v size: 3
 destructing 
 destructing 
 destructing 

Answer 1

After tinkering with it a bit with both GCC 4.7 and 4.8, it seems that it is indeed a bug in 4.7, which only appears when the class' destructor is not marked noexcept:

struct Foo {
  Foo() {}
  ~Foo() noexcept {}
  Foo(Foo&&) noexcept { std::cout << "move constructor" << std::endl; }
  Foo(const Foo&) noexcept { std::cout << "copy constructor" << std::endl; }
};

int main() {
  std::vector<Foo> v;
  v.reserve(2);
  v.emplace_back();
  v.emplace_back();
  v.emplace_back();
}

GCC 4.7 displays:

move constructor
move constructor

If we remove noexcept from the destructor:

struct Foo {
  Foo() {}
  ~Foo() {}
  Foo(Foo&&) noexcept { std::cout << "move constructor" << std::endl; }
  Foo(const Foo&) noexcept { std::cout << "copy constructor" << std::endl; }
};

GCC 4.7 displays:

copy constructor
copy constructor

GCC 4.8 uses the move constructor in both cases.