STL源码剖析 容器 stl_queue.h

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queue

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stack 是一种配接器(adapter)，以某种容器作为底部结构，改变其接口，使之符合"先进先出"的特性。

SGI STL 默认以 deque 为 stack 底部结构

没有遍历行为，没有遍历器

示例：

#include <queue>
#include <list>
#include <iostream>
#include <algorithm>
using namespace std;

int main(){
	queue<int, list<int> >iqueue;
	iqueue.push(1);
	iqueue.push(2);
	cout << iqueue.size() << endl
		 << iqueue.front() << endl;
}

源码：

#ifndef __SGI_STL_INTERNAL_QUEUE_H
#define __SGI_STL_INTERNAL_QUEUE_H

__STL_BEGIN_NAMESPACE

#ifndef __STL_LIMITED_DEFAULT_TEMPLATES
template <class T, class Sequence = deque<T> >//默认以 deque 为底层容器
#else
template <class T, class Sequence>
#endif
class queue {
  friend bool operator== __STL_NULL_TMPL_ARGS (const queue& x, const queue& y);
  friend bool operator< __STL_NULL_TMPL_ARGS (const queue& x, const queue& y);
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:
  //以下完全利用 Sequence c 的操作完成 queue 的操作
  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(); }
  //修改接口使符合 queue "前进先出"的条件
  void push(const value_type& x) { c.push_back(x); }
  void pop() { c.pop_front(); }
};

template <class T, class Sequence>
bool operator==(const queue<T, Sequence>& x, const queue<T, Sequence>& y) {
  return x.c == y.c;
}

template <class T, class Sequence>
bool operator<(const queue<T, Sequence>& x, const queue<T, Sequence>& y) {
  return x.c < y.c;
}

priority_queue

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priority_queue 是一个 queue ，所以只允许在底端加入元素，并从顶端取出元素，

priority_queue 带有权值观念，其内的元素并非依照被推入的次序排列，而是自动依照元素的权值排列。

priority_queue 以底部容器为依据，再加上 heap 处理规则，缺省是以 vector 为底层容器

示例：

int main(){
	int ia[] = {0,1,2,3,4,8,9,3,5};
	priority_queue<int> ipq(ia, ia + 9);
	while(!ipq.empty()){
		cout << ipq.top() << ' ';
		ipq.pop();
	}
	cout << endl;
}

源码：

#ifndef __STL_LIMITED_DEFAULT_TEMPLATES
template <class T, class Sequence = vector<T>, //底部默认采用 vector 容器
          class Compare = less<typename Sequence::value_type> > //默认权值大的排在前面
#else
template <class T, class Sequence, class Compare>
#endif
class  priority_queue {
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
  Compare comp; //元素大小比较标准
public:
  priority_queue() : c() {}
  explicit priority_queue(const Compare& x) :  c(), comp(x) {}

#ifdef __STL_MEMBER_TEMPLATES
  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)
    : c(first, last) { make_heap(c.begin(), c.end(), comp); }
#else /* __STL_MEMBER_TEMPLATES */
  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)
    : c(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 {
	  //无利用底层容器的 push_back() 将新元素推入末端，再重排 heap()
      c.push_back(x);
      push_heap(c.begin(), c.end(), comp);
    }
    __STL_UNWIND(c.clear());
  }
  void pop() {
    __STL_TRY {
	  //将权值最大或最小放在尾端
      pop_heap(c.begin(), c.end(), comp);
	  //将用底层容器的 pop_back() 弹出
      c.pop_back();
    }
    __STL_UNWIND(c.clear());
  }
};

// no equality is provided

__STL_END_NAMESPACE

#endif /* __SGI_STL_INTERNAL_QUEUE_H */

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STL源码剖析 容器 stl_queue.h