Why is C++ STL implementation is written like this

[noobofcpp]

Why they use some kind of crazy naming convension and lot of underscores?

	// constructors
	vector_impl(_Mytype_t% _Right)
		{	// construct by copying _Right
		for (size_type _Idx = _Buy(_Right.size()); 0 <= --_Idx; )
			_Myarray[_Idx] = _Mymake_t::make_value(_Right.at(_Idx));
		_Mysize = _Right.size();
		}

	explicit vector_impl(size_type _Count)
		{	// construct from _Count * value_type()
		_Mysize = _Fill_n(0, _Buy(_Count), value_type());
		}

	vector_impl(size_type _Count, value_type _Val)
		{	// construct from _Count * _Val
		_Mysize = _Fill_n(0, _Buy(_Count), _Val);
		}

	template<typename _InIt_t>
		vector_impl(_InIt_t _First, _InIt_t _Last)
		{	// construct from [_First, _Last)
		_Construct(_First, _Last, _Iter_category(_First));
		}

	template<typename _InIt_t>
		void _Construct(_InIt_t _Count, _InIt_t _Val,
			_Int_iterator_tag%)
		{	// initialize with _Count * _Val
		_Mysize = _Fill_n(0, _Buy((size_type)_Count), (value_type)_Val);
		}

	template<typename _InIt_t>
		void _Construct(_InIt_t _First, _InIt_t _Last,
			input_iterator_tag%)
		{	// initialize with [_First, _Last), input iterators
		_Buy(_First != _Last ? 1 : 0);	// buy at least one if non-empty
		for (; _First != _Last; ++_First)
			insert_n(size(), 1, (value_type)*_First);
		}

	template<typename _InIt_t>
		void _Construct(_InIt_t _First, _InIt_t _Last,
			forward_iterator_tag%)
		{	// initialize with [_First, _Last), forward iterators
		size_type _Size = cliext::distance(_First, _Last);

		_Buy(_Size);
		for (size_type _Idx = 0; _Idx < _Size; ++_Idx, ++_First)
			_Myarray[_Idx] = _Mymake_t::make_value(value_type(*_First));
		_Mysize = _Size;
		}

[2kaud]

Variables starting with _ are reserved for use by the C++ language implementers for library usage. Although legal, you should never yourself use a variable that starts with _.