//SGI STL以deque作为缺省情况下的stack底部结构,stack没有迭代器，不提供遍历功能//queue的实现类似stack，也是以deque作为缺省底层结构template <class T,class Sequence=deque<T>>class stack{    friend bool operator==__STL_NULL_TMPL_ARGS(const stack&, const stack&);    friend bool operator<__STL_NULL_TMPL_ARGS(const stack&, const stack&);public:    typedef typename Sequence::value_type value_type;    typedef typename Sequence::size_type size_type;    typedef typename Sequence::reference reference;    typedef typename Sequence::const_reference const_reference;protected:    Sequence c;//底层容器public:    bool empty()const{ return c.empty(); }    size_type size()const{ return c.size() }    reference top(){ return c.back; }    const_reference top()const{ return c.back(); }    void push(const value_type& x){ c.push_back(x); }    void pop(){ c.pop_back(); }};template<class T,class Sequence>bool operator==(const stack<T, Sequence>&x, const stack<T, Sequence>&y){    return x.c == y.c;}template<class T, class Sequence>bool operator<(const stack<T, Sequence>&x, const stack<T, Sequence>&y){    return x.c < y.c;}