STL学习笔记——1.queue

STL学习笔记——1.queue

     之前被学长坑了，非要模拟队列，以至于现在完全看不懂网上用STL写的代码，只有现学了(╯‵□′)╯︵┻━┻。

以下资料主要参考网站http://www.cplusplus.com/reference/queue/

classtemplate

<queue>

std::queue

template <class T, class Container =deque<T> > class queue;
FIFOqueue
queues area 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 containerand extracted from the other.
queues are implemented as containers adaptors, which are classesthat use an encapsulated object of a specific container class as its
underlyingcontainer, providing a specific set of member functions to access itselements. Elements are
pushed into the "back" of thespecific container and popped from its
"front".

The underlying container may be one of the standard container class template orsome other specifically designed container class. This underlying containershall support at least the following operations:
empty
size
front
back
push_back
pop_front
队列的特点如上文，简单而言就是FIFO，即First
In
First
Out，也就是先入先出。主要形式要注意：

●头文件 #include<queue>(或者直接写#include<bits/stdc++.h>)

●声明：

❶如果之前已经声明了命名空间：using namespace std;

则直接写：queue<变量类型（如int||char）>
变量名称（选一个自己喜欢的就好罒ω罒）

❷如果之前没有声明命名空间，则写：

std::queue<变量类型（如int||char）>
变量名称（选一个自己喜欢的就好罒ω罒）

●常用函数：

                   ❶empty:

std::queue::empty

bool empty() const;
Test whethercontainer is empty
Returns whether the
queue is empty: i.e.whether its
size is
zero.

This member function effectively calls member empty of the
underlyingcontainer object.

Parameters

None
Return Value
true if the underlyingcontainer's size is 0, false otherwise.

即判断队列是否为空。这样说比较抽象，还是直接用代码说明吧。

// queue::empty
#include <iostream>       // std::cout
#include <queue>          // std::queue

int main ()
{
std::queue<int> myqueue;
int sum (0);

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

while (!myqueue.empty())
{
sum += myqueue.front();
myqueue.pop();
}

std::cout << "total: " << sum << '\n';

return 0;
}

❷pop&&push
std::queue::pop

void pop();

Remove next element

Removes the next element in the queue, effectively reducing its size by one.

The element removed is the "oldest" element in the queue whose value can be retrieved by calling member queue::front.

This calls the removed element's destructor.

This member function effectively calls the member function pop_front of the underlying container object.

std::queue::push

·        C++98

·        C++11

·         

void push (const value_type& val);

void push (const value_type& val);

void push (value_type&& val);

Insert element
Inserts a new element at the end of the
queue, afterits current last element. The content of this new element is initialized
to val.

This member function effectively calls the member function push_back of the
underlying container object.

Parameters

val
Value to which the inserted element is initialized.

Member type value_type is the type of the elements in the container (defined as an aliasof the first class template parameter,
T).

Return value

none

push是把元素推入队列，而pop与之相反是将元素赶出队列（既然这里用了赶出，肯定是队列中不再有这个元素了）
还是直接放代码：

// queue::push/pop
#include <iostream>       // std::cin, std::cout
#include <queue>          // std::queue

int main ()
{
std::queue<int> myqueue;
int myint;

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

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

std::cout << "myqueue contains: ";
while (!myqueue.empty())
{
std::cout << ' ' << myqueue.front();
myqueue.pop();
}
std::cout << '\n';

return 0;
}

❸front&&back

std::queue::front

·        C++98

·        C++11

·         

      value_type& front();

const value_type& front() const;

      reference& front();

const_reference& front() const;

Access next element
Returns a reference to the nextelement in the
queue.

The next element isthe "oldest" element in the queue and the same element
that is popped out from the queue when
queue::pop is called.

This member function effectively calls member front of the
underlyingcontainer object.

Parameters

none

Return value

A reference to the next element in the
queue.

·        C++98

·        C++11

·         
Member type value_type is the type of the elements inthe container (defined as an alias of the first class template parameter,
T).
如上文：front 就是排在最前面的那个元素还是很形象的╮(╯▽╰)╭。

// queue::front
#include <iostream>       // std::cout
#include <queue>          // std::queue

int main ()
{
std::queue<int> myqueue;

myqueue.push(77);
myqueue.push(16);

myqueue.front() -= myqueue.back();    // 77-16=61

std::cout << "myqueue.front() is now " << myqueue.front() << '\n';

return 0;
}

/*Output:
myqueue.front() is now 61*/

std::queue::back

·        C++98

·        C++11

·         

      value_type& back();

const value_type& back() const;

      reference& back();

const_reference& back() const;

Access last element
Returns a reference to the last elementin the
queue. Thisis the "newest" element in the queue (i.e. the last element pushedinto
the queue).

This member function effectively calls member back of theunderlying container
object.

Parameters

none

Return value

A reference to the last element in the
queue.

·        C++98

·        C++11

·         
Member type value_type is the type of the elements inthe container (defined as an alias of the first class template parameter,
T).
如上文，back与front 相反
还是直接上代码：

// queue::back
#include <iostream>       // std::cout
#include <queue>          // std::queue

int main ()
{
std::queue<int> myqueue;

myqueue.push(12);
myqueue.push(75);   // this is now the back

myqueue.back() -= myqueue.front();

std::cout << "myqueue.back() is now " << myqueue.back() << '\n';

return 0;
}

/*Output:
myqueue.back() is now 63*/

❹size

std::queue::size

size_type size() const;

Return size
Returns the number of elements in the
queue.

This member function effectively calls member size of theunderlying container
object.

Parameters

none

Return Value

Thenumber of elements in the underlying container.

Member type size_type is an unsigned integral type.

计算队列大小？（或者是不是该称为长度）

// queue::size
#include <iostream>       // std
b374
::cout
#include <queue>          // std::queue

int main ()
{
std::queue<int> myints;
std::cout << "0. size: " << myints.size() << '\n';

for (int i=0; i<5; i++) myints.push(i);
std::cout << "1. size: " << myints.size() << '\n';

myints.pop();
std::cout << "2. size: " << myints.size() << '\n';

return 0;
}

Output:

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

❺swap

std::queue::swap

void swap (queue& x) noexcept(/*see below*/);

Swap contents
Exchanges the contents of the container adaptor (

*this

) by those of
x.

This member function calls the non-member function swap(unqualified) to swap the
underlying containers.

The

noexcept

specifier matches the
swapoperation on the
underlying container.

Parameters

x
Another queue container adaptor
of the same type (i.e., instantiated with thesame template parameters, T and
Container). Sizesmay differ.

Return value

none

swap就是交换，交换两个队列：

// queue::swap
#include <iostream>       // std::cout
#include <queue>          // std::queue

int main ()
{
std::queue<int> foo,bar;
foo.push (10); foo.push(20); foo.push(30);
bar.push (111); bar.push(222);

foo.swap(bar);

std::cout << "size of foo: " << foo.size() << '\n';
std::cout << "size of bar: " << bar.size() << '\n';

return 0;
}

Output:

size of foo: 2 size of bar: 3