因为只有一个堆叠端口，这也是在口腔进入口。

可以在堆栈中只能操作，你不能访问其它元件的堆叠。器。
Stack的实现是依赖其它容器的。用deque做底层数据结构。这种实现。在STL中往往不称做container容器，往往被归类为container adapter容器适配器。deque是双向开口的数据结构，功能远强大于栈，仅仅需简单分装就可以做成栈。

用其它容器做底层数据结构也但是实现栈，vector、list也支持empty、size、back、push_back、pop_back操作。我想用deque是一种折中吧！假设用vector在又一次分配空间时须要拷贝原来空间的元素。释放原来空间。假设使用list的话。每一次push_back、pop_back都涉及空间的分配和释放。

G++ 2.91.57，cygnus\cygwin-b20\include\g++\stl_stack.h 完整列表
/*** Copyright (c) 1994* Hewlett-Packard Company** Permission to use, copy, modify, distribute and sell this software* and its documentation for any purpose is hereby granted without fee,* provided that the above copyright notice appear in all copies and* that both that copyright notice and this permission notice appear* in supporting documentation.  Hewlett-Packard Company makes no* representations about the suitability of this software for any* purpose.  It is provided "as is" without express or implied warranty.*** Copyright (c) 1996,1997* Silicon Graphics Computer Systems, Inc.** Permission to use, copy, modify, distribute and sell this software* and its documentation for any purpose is hereby granted without fee,* provided that the above copyright notice appear in all copies and* that both that copyright notice and this permission notice appear* in supporting documentation.  Silicon Graphics makes no* representations about the suitability of this software for any* purpose.  It is provided "as is" without express or implied warranty.*//* NOTE: This is an internal header file, included by other STL headers.*   You should not attempt to use it directly.*/#ifndef __SGI_STL_INTERNAL_STACK_H
#define __SGI_STL_INTERNAL_STACK_H__STL_BEGIN_NAMESPACE#ifndef __STL_LIMITED_DEFAULT_TEMPLATES
template <class T, class Sequence = deque<T> >
#else
template <class T, class Sequence>
#endif
class stack {//友元函数，后面会展开的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deque
public:// 下面全然利用 Sequence c 的操作，完毕 stack 的操作。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;
}__STL_END_NAMESPACE#endif /* __SGI_STL_INTERNAL_STACK_H */// Local Variables:
// mode:C++
// End: