元素类型C++ 标准模板库STL 队列 queue 使用方法与应用介绍（一）

发一下牢骚和主题无关：

    queue

    queue模板类的定义在<queue>头文件中。

    与stack模板类很相似，queue模板类也需要两个模板参数，一个是元素类型，一个容器类型，元素类型是必要的，容器类型是可选的，默以为deque类型。

    定义queue对象的示例代码如下：

    queue<int> q1;

    queue<double> q2;

    queue的基本操作有：

    

    入队，如例：q.push(x); 将x接到队列的末了。

    出队，如例：q.pop(); 弹出队列的第一个元素，注意，并不会返回被弹出元素的值。

    拜访队首元素，如例：q.front()，即最早被压入队列的元素。

    拜访队尾元素，如例：q.back()，即最后被压入队列的元素。

    判断队列空，如例：q.empty()，当队列空时，返回true。

    拜访队列中的元素个数，如例：q.size()

    

    

    

std::queue

    

FIFO queue

    

    queue

    

    s are a type of container adaptor, specifically designed to operate in a FIFO context (first-in first-out), where elements are inserted into one end of the container and extracted from the other.

    

    queue

    

    s are implemented as

    

    containers adaptors

    

    , which are classes that use an encapsulated object of a specific container class as its

    

    underlying container

    

    , providing a specific set of member functions to access its elements. Elements are

    

    pushed

    

    into the

    

    "back"

    

    of the specific container and

    

    popped

    

    from its

    

    "front"

    

    .

    The underlying container may be one of the standard container class template or some other specifically designed container class. The only requirement is that it supports the following operations:

    

• front()
• back()
• push_back()
• pop_front()

    Therefore, the standard container class templates

     deque

    and

    list

    can be used. By default, if no container class is specified for a particular

    

    queue

    

    class, the standard container class template

     deque

    is used.

    In their implementation in the C++ Standard Template Library, queues take two template parameters:

template < class T, class Container = deque<T> > class queue;

Where the template parameters have the following meanings:

    

• T: Type of the elements.
• Container: Type of the underlying container object used to store and access the elements.

    In the reference for the queue member functions, these same names are assumed for the template parameters.

     

    

    

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#include <iostream>
#include <queue>
#include <string>
using namespace std;
void test_empty()
{
  queue<int> myqueue;
  int sum (0);

  for (int i=1;i<=10;i++) myqueue.push(i);

  while (!myqueue.empty())
  {
     sum += myqueue.front();
     myqueue.pop();
  }
    cout << "total: " << sum << endl;
}//运行结果： total： 55
void test_pop()
{
  queue<int> myqueue;
  int myint;

  cout << "\nPlease enter some integers (enter 0 to end):\n";

  do
  {
    cin >> myint;
    myqueue.push (myint);
  } while (myint);

  cout << "myqueue contains: ";
  while (!myqueue.empty())
  {
    cout << " " << myqueue.front();
    myqueue.pop();
  }
}
/********
运行结果：
Please enter some integers (enter 0 to end):
512
605
420
517
532
0
myqueue contains:  512 605 420 517 532 0
********/
void test_size()
{
  queue<int> myints;
  cout << "0. size: " << (int) myints.size() << endl;

  for (int i=0; i<5; i++) myints.push(i);
  cout << "1. size: " << (int) myints.size() << endl;

  myints.pop();
  cout << "2. size: " << (int) myints.size() << endl;
}
/****
运行结果：
0. size: 0
1. size: 5
2. size: 4
****/
int main()
{
    test_empty();
    cout<<"\n***********************************************\n";
    test_size();
    cout<<"\n***********************************************\n";
    test_pop();
    cout<<"\n***********************************************\n";
    queue<string> q;

    // insert three elements into the queue
    q.push("These ");
    q.push("are ");
    q.push("more than ");
    //cout << "number of elements in the queue: " << q.size()<< endl;

    // read and print two elements from the queue
    cout << q.front();
    q.pop();
    cout << q.front();
    q.pop();
    //cout << "number of elements in the queue: " << q.size()<< endl;

    // insert two new elements
    q.push("four ");
    q.push("words!");
    //cout << "\nnumber of elements in the queue: " << q.size()<< endl;
    // skip one element
    q.pop();

    // read and print two elements
    cout << q.front();
    q.pop();
    cout << q.front() << endl;
    q.pop();

    // print number of elements in the queue
    cout << "number of elements in the queue: " << q.size()<< endl;
}
/*******
*运行结果：
total: 55

***********************************************
0. size: 0
1. size: 5
2. size: 4

***********************************************

Please enter some integers (enter 0 to end):
512
605
420
517
532
0
myqueue contains:  512 605 420 517 532 0
***********************************************
These are four words!
number of elements in the queue: 0

Process returned 0 (0x0)   execution time : 33.512 s
Press any key to continue.

********/

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