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 | #if __cplusplus >= 201103L
  template<typename _Tp, typename _Alloc>
    template<typename... _Args>
#if __cplusplus > 201402L
      _GLIBCXX20_CONSTEXPR
      typename vector<_Tp, _Alloc>::reference
#else
      void
#endif
      vector<_Tp, _Alloc>::
      emplace_back(_Args&&... __args)
      {
	if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
	  {
	    _GLIBCXX_ASAN_ANNOTATE_GROW(1);
	    _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
				     std::forward<_Args>(__args)...);
	    ++this->_M_impl._M_finish;
	    _GLIBCXX_ASAN_ANNOTATE_GREW(1);
	  }
	else
	  _M_realloc_insert(end(), std::forward<_Args>(__args)...);
#if __cplusplus > 201402L
	return back();
#endif
      }
#endif
#if __cplusplus >= 201103L
  template<typename _Tp, typename _Alloc>
    template<typename... _Args>
      _GLIBCXX20_CONSTEXPR
      void
      vector<_Tp, _Alloc>::
      _M_realloc_insert(iterator __position, _Args&&... __args)
#else
  template<typename _Tp, typename _Alloc>
    void
    vector<_Tp, _Alloc>::
    _M_realloc_insert(iterator __position, const _Tp& __x)
#endif
    {
      // 计算新容量  
      const size_type __len =
	_M_check_len(size_type(1), "vector::_M_realloc_insert");
      pointer __old_start = this->_M_impl._M_start;
      pointer __old_finish = this->_M_impl._M_finish;
      const size_type __elems_before = __position - begin();
      pointer __new_start(this->_M_allocate(__len));
      pointer __new_finish(__new_start);
      __try
	{
	  // The order of the three operations is dictated by the C++11
	  // case, where the moves could alter a new element belonging
	  // to the existing vector.  This is an issue only for callers
	  // taking the element by lvalue ref (see last bullet of C++11
	  // [res.on.arguments]).
	  _Alloc_traits::construct(this->_M_impl,
				   __new_start + __elems_before,
#if __cplusplus >= 201103L
				   std::forward<_Args>(__args)...);
#else
				   __x);
#endif
	  __new_finish = pointer();
#if __cplusplus >= 201103L
	  if _GLIBCXX17_CONSTEXPR (_S_use_relocate())
	    {
	      __new_finish = _S_relocate(__old_start, __position.base(),
					 __new_start, _M_get_Tp_allocator());
	      ++__new_finish;
	      __new_finish = _S_relocate(__position.base(), __old_finish,
					 __new_finish, _M_get_Tp_allocator());
	    }
	  else
#endif
	    {
	      __new_finish
		= std::__uninitialized_move_if_noexcept_a
		(__old_start, __position.base(),
		 __new_start, _M_get_Tp_allocator());
	      ++__new_finish;
	      __new_finish
		= std::__uninitialized_move_if_noexcept_a
		(__position.base(), __old_finish,
		 __new_finish, _M_get_Tp_allocator());
	    }
	}
      __catch(...)
	{
	  if (!__new_finish)
	    _Alloc_traits::destroy(this->_M_impl,
				   __new_start + __elems_before);
	  else
	    std::_Destroy(__new_start, __new_finish, _M_get_Tp_allocator());
	  _M_deallocate(__new_start, __len);
	  __throw_exception_again;
	}
#if __cplusplus >= 201103L
      if _GLIBCXX17_CONSTEXPR (!_S_use_relocate())
#endif
	std::_Destroy(__old_start, __old_finish, _M_get_Tp_allocator());
      _GLIBCXX_ASAN_ANNOTATE_REINIT;
      _M_deallocate(__old_start,
		    this->_M_impl._M_end_of_storage - __old_start);
      this->_M_impl._M_start = __new_start;
      this->_M_impl._M_finish = __new_finish;
      this->_M_impl._M_end_of_storage = __new_start + __len;
    }
      _GLIBCXX20_CONSTEXPR
      size_type
      _M_check_len(size_type __n, const char* __s) const
      {
	if (max_size() - size() < __n)
	  __throw_length_error(__N(__s));
    // 新容量 = 当前大小 + max(当前大小, 1)
	const size_type __len = size() + (std::max)(size(), __n);
	return (__len < size() || __len > max_size()) ? max_size() : __len;
      }
 |