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我试图使用自定义分配器std::vector<char>,但我注意到std::vector不需要/使用我的分配器中的任何成员函数.这怎么可能？

#include <vector>

struct A : private std::allocator<char> {
   typedef std::allocator<char> alloc;
   using alloc::value_type;
   using alloc::pointer;
   using alloc::const_pointer;
   using alloc::difference_type;
   using alloc::size_type;
   using alloc::rebind;
   // member functions have been removed, since the program compiles without them
};

int main() {
    std::vector<char, A> v;
    v.resize(4000);
    for (auto& c : v)
      if (c)
         return 1; // never happens in my environment
   return 0; // all elements initialized to 0. How is this possible?
}

我正在使用在线C++ 11编译器(LiveWorkSpace)尝试上述程序,提供g ++ 4.7.2,4.8和4.6.3. …