STL学习--queue priority_queue

简介

queue是一种先入先出（FIFO）的数据结构，它有两个出口，允许从底端加入元素，从顶端移除元素。STL底层默认基于deque容器实现，可在创建是更改list：

queue< string, list<string> > str_queue; // 由list实现的queue

priority_queue是拥有权值的queue，其内部元素不是按照添加的顺序排列，而是按照权值排列（权值默认为元素值），权值高的拍在前边。STL底层默认基于vector容器实现，可以在创建是更改为deque：

queue< string, list<string> > str_queue; // 由list实现的queue

特性

queue先入先出（FIFO）。

queue由于需要支持pop_front，因此不能有vector容器实现。

queue不提供遍历功能，没有迭代器。

priority_queue权值高先出。

priority_queue支持随机访问功能，因此建立在vector或deque容器上。

常用操作

q.empty()如果队列为空，则返回 true，否则返回 falseq.size()返回队列中元素的个数q.pop()删除队首元素，但不返回其值q.front()返回队首元素的值，但不删除该元素

该操作只适用于队列

q.back()返回队尾元素的值，但不删除该元素

该操作只适用于队列

q.top()

返回具有最高优先级的元素值，但不删除该素

该操作只适用于优先级队列

q.push(item)

对于 queue，在队尾压入一个新元素，对于 priority_quue，在基于优先级的适当位置插入新元素

源码（STL3.3）

/* * * 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_QUEUE_H#define __SGI_STL_INTERNAL_QUEUE_H#include <sequence_concepts.h>__STL_BEGIN_NAMESPACE// Forward declarations of operators < and ==, needed for friend declaration.template <class _Tp,           class _Sequence __STL_DEPENDENT_DEFAULT_TMPL(deque<_Tp>) >class queue;template <class _Tp, class _Seq>inline bool operator==(const queue<_Tp, _Seq>&, const queue<_Tp, _Seq>&);template <class _Tp, class _Seq>inline bool operator<(const queue<_Tp, _Seq>&, const queue<_Tp, _Seq>&);template <class _Tp, class _Sequence>class queue {  // requirements:  __STL_CLASS_REQUIRES(_Tp, _Assignable);  __STL_CLASS_REQUIRES(_Sequence, _FrontInsertionSequence);  __STL_CLASS_REQUIRES(_Sequence, _BackInsertionSequence);  typedef typename _Sequence::value_type _Sequence_value_type;  __STL_CLASS_REQUIRES_SAME_TYPE(_Tp, _Sequence_value_type);#ifdef __STL_MEMBER_TEMPLATES   template <class _Tp1, class _Seq1>  friend bool operator== (const queue<_Tp1, _Seq1>&,                          const queue<_Tp1, _Seq1>&);  template <class _Tp1, class _Seq1>  friend bool operator< (const queue<_Tp1, _Seq1>&,                         const queue<_Tp1, _Seq1>&);#else /* __STL_MEMBER_TEMPLATES */  friend bool __STD_QUALIFIER  operator== __STL_NULL_TMPL_ARGS (const queue&, const queue&);  friend bool __STD_QUALIFIER  operator<  __STL_NULL_TMPL_ARGS (const queue&, const queue&);#endif /* __STL_MEMBER_TEMPLATES */public:  typedef typename _Sequence::value_type      value_type;  typedef typename _Sequence::size_type       size_type;  typedef          _Sequence                  container_type;  typedef typename _Sequence::reference       reference;  typedef typename _Sequence::const_reference const_reference;protected:  _Sequence c;public:  queue() : c() {}  explicit queue(const _Sequence& __c) : c(__c) {}  bool empty() const { return c.empty(); }  size_type size() const { return c.size(); }  reference front() { return c.front(); }  const_reference front() const { return c.front(); }  reference back() { return c.back(); }  const_reference back() const { return c.back(); }  void push(const value_type& __x) { c.push_back(__x); }  void pop() { c.pop_front(); }};template <class _Tp, class _Sequence>bool operator==(const queue<_Tp, _Sequence>& __x, const queue<_Tp, _Sequence>& __y){  return __x.c == __y.c;}template <class _Tp, class _Sequence>booloperator<(const queue<_Tp, _Sequence>& __x, const queue<_Tp, _Sequence>& __y){  return __x.c < __y.c;}#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDERtemplate <class _Tp, class _Sequence>booloperator!=(const queue<_Tp, _Sequence>& __x, const queue<_Tp, _Sequence>& __y){  return !(__x == __y);}template <class _Tp, class _Sequence>bool operator>(const queue<_Tp, _Sequence>& __x, const queue<_Tp, _Sequence>& __y){  return __y < __x;}template <class _Tp, class _Sequence>bool operator<=(const queue<_Tp, _Sequence>& __x, const queue<_Tp, _Sequence>& __y){  return !(__y < __x);}template <class _Tp, class _Sequence>bool operator>=(const queue<_Tp, _Sequence>& __x, const queue<_Tp, _Sequence>& __y){  return !(__x < __y);}#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */template <class _Tp,           class _Sequence __STL_DEPENDENT_DEFAULT_TMPL(vector<_Tp>),          class _Compare          __STL_DEPENDENT_DEFAULT_TMPL(less<typename _Sequence::value_type>) >class priority_queue {  // requirements:  __STL_CLASS_REQUIRES(_Tp, _Assignable);  __STL_CLASS_REQUIRES(_Sequence, _Sequence);  __STL_CLASS_REQUIRES(_Sequence, _RandomAccessContainer);  typedef typename _Sequence::value_type _Sequence_value_type;  __STL_CLASS_REQUIRES_SAME_TYPE(_Tp, _Sequence_value_type);  __STL_CLASS_BINARY_FUNCTION_CHECK(_Compare, bool, _Tp, _Tp);public:  typedef typename _Sequence::value_type      value_type;  typedef typename _Sequence::size_type       size_type;  typedef          _Sequence                  container_type;  typedef typename _Sequence::reference       reference;  typedef typename _Sequence::const_reference const_reference;protected:  _Sequence c;  _Compare comp;public:  priority_queue() : c() {}  explicit priority_queue(const _Compare& __x) :  c(), comp(__x) {}  priority_queue(const _Compare& __x, const _Sequence& __s)     : c(__s), comp(__x)     { make_heap(c.begin(), c.end(), comp); }#ifdef __STL_MEMBER_TEMPLATES  template <class _InputIterator>  priority_queue(_InputIterator __first, _InputIterator __last)     : c(__first, __last) { make_heap(c.begin(), c.end(), comp); }  template <class _InputIterator>  priority_queue(_InputIterator __first,                  _InputIterator __last, const _Compare& __x)    : c(__first, __last), comp(__x)     { make_heap(c.begin(), c.end(), comp); }  template <class _InputIterator>  priority_queue(_InputIterator __first, _InputIterator __last,                 const _Compare& __x, const _Sequence& __s)  : c(__s), comp(__x)  {     c.insert(c.end(), __first, __last);    make_heap(c.begin(), c.end(), comp);  }#else /* __STL_MEMBER_TEMPLATES */  priority_queue(const value_type* __first, const value_type* __last)     : c(__first, __last) { make_heap(c.begin(), c.end(), comp); }  priority_queue(const value_type* __first, const value_type* __last,                  const _Compare& __x)     : c(__first, __last), comp(__x)    { make_heap(c.begin(), c.end(), comp); }  priority_queue(const value_type* __first, const value_type* __last,                  const _Compare& __x, const _Sequence& __c)    : c(__c), comp(__x)   {     c.insert(c.end(), __first, __last);    make_heap(c.begin(), c.end(), comp);  }#endif /* __STL_MEMBER_TEMPLATES */  bool empty() const { return c.empty(); }  size_type size() const { return c.size(); }  const_reference top() const { return c.front(); }  void push(const value_type& __x) {    __STL_TRY {      c.push_back(__x);       push_heap(c.begin(), c.end(), comp);    }    __STL_UNWIND(c.clear());  }  void pop() {    __STL_TRY {      pop_heap(c.begin(), c.end(), comp);      c.pop_back();    }    __STL_UNWIND(c.clear());  }};// no equality is provided__STL_END_NAMESPACE#endif /* __SGI_STL_INTERNAL_QUEUE_H */// Local Variables:// mode:C++// End: