std :: includes（）函数以及C ++中的示例

灰太狼 2023-03-05 13:28 14阅读 0赞

## std :: includes() **(**std::includes()**)** ##

**includes()** is a very helpful STL function which checks whether a sorted range includes another sorted range or not. In other words, it helps to check whether a set is a subset of another set or not considering the set is ordered. Needless to say, both range/set must be ordered in the same fashion, i.e., either both in ascending or both in descending order. Otherwise, it will fail to detect.

**include()**是一个非常有用的STL函数，它检查一个排序范围是否包括另一个排序范围。 换句话说，它有助于检查一个集合是否是另一个集合的子集，或者不考虑该集合是有序的。 不用说，两个范围/组都必须以相同的方式排序，即，要么以升序要么都以降序排序。 否则，它将无法检测。

It has two kind of usages:

它有两种用法：

### 1)默认比较器 **(**1) Default comparator**)** ###

**Syntax:**

**句法：**

bool includes(
        InputIterator1 first1, 
        InputIterator1 last1,
        InputIterator2 first2, 
        InputIterator2 last2);

Where,

哪里，

*  InputIterator1 first1 \- starting range of the container which will include
    
    InputIterator1 first1-容器的起始范围，其中包括
 *  InputIterator1 last1 \- ending range of the container which will include
    
    InputIterator1 last1-容器的结束范围，其中包括
 *  InputIterator2 first2 \- starting range of the container which will be included
    
    InputIterator2 first2-将包含的容器的起始范围
 *  InputIterator2 last2 \- starting range of the container which will be included
    
    InputIterator2 last2-将包含的容器的起始范围

So basically *\[first1,last1\]* defines the container which will include contents and *\[first2, last2\]* defines the container whose contents will be included.

因此，基本上*\[first1，last1\]*定义了容器，其中将包括内容和*\[first2，last2\]*定义，其内容将被包括在容器中。

The function returns true if the container1 includes container 2, False otherwise. Since, default comparator is used, two elements, a and b are considered equivalent if *(!(a<b) && !(b<a))*.

如果container1包含容器2，则该函数返回true，否则返回False。 由于使用了默认比较器，因此如果*(！(a <b)&&！(b <a))，*则将两个元素a和b视为等效。

For example:

例如：

If container1 is \[3, 5, 7, 9\] and container2 is \[5, 9\] then container1 includes container2 and thus the include function will return true;

如果container1为\[3，5，7，9\]，container2为\[5，9\]，则container1包含container2，因此include函数将返回true；

But if the container was \[9, 5\] it would have retuned false because when 9 is found the range is already covered in container1, no 5 is there after 9 in container 1. Also, if container2 is \[5,8\] it will return false as container1 does not container 8 at all.

但是，如果容器为\[9，5\]，它将被重新设置为false，因为当找到9时，容器1中已经覆盖了该范围，那么容器1中的9之后便没有5。此外，如果容器2为\[5,8\]，它将返回false，因为container1根本不包含容器8。

Below is the implementation:

下面是实现：

**Case 1: arr1=\[3,5,7,9\], arr2=\[5,9\]**

**情况1：arr1 = \[3,5,7,9\]，arr2 = \[5,9\]**

#include <bits/stdc++.h>
    using namespace std;
    
    int main()
    {
        vector<int> arr1{ 3, 5, 7, 9 };
        vector<int> arr2{ 5, 9 };
    
        if (includes(arr1.begin(), arr1.end(), arr2.begin(), arr2.end()))
            cout << "arr1 contains arr2\n";
        else
            cout << "arr1 doesn't contain arr2\n";
        
        return 0;
    }

**Output:**

**输出：**

arr1 contains arr2

**Case 2: arr2=\[3,5,7,9\], arr2=\[9,5\]**

**情况2：arr2 = \[3,5,7,9\]，arr2 = \[9,5\]**

#include <bits/stdc++.h>
    using namespace std;
    
    int main()
    {
        vector<int> arr1{ 3, 5, 7, 9 };
        vector<int> arr2{ 9, 5 };
    
        if (includes(arr1.begin(), arr1.end(), arr2.begin(), arr2.end()))
            cout << "arr1 contains arr2\n";
        else
            cout << "arr1 doesn't contain arr2\n";
    
        return 0;
    }

**Output:**

**输出：**

arr1 doesn't contain arr2

**Case 3: arr2=\[3,5,7,9\], arr2=\[5, 8\]**

**情况3：arr2 = \[3,5,7,9\]，arr2 = \[5，8\]**

#include <bits/stdc++.h>
    using namespace std;
    
    int main()
    {
        vector<int> arr1{ 3, 5, 7, 9 };
        vector<int> arr2{ 5, 8 };
    
        if (includes(arr1.begin(), arr1.end(), arr2.begin(), arr2.end()))
            cout << "arr1 contains arr2\n";
        else
            cout << "arr1 doesn't contain arr2\n";
    
        return 0;
    }

**Output:**

**输出：**

arr1 doesn't contain arr2

### 2)使用用户定义的比较器 **(**2) Using user-defined comparator**)** ###

We can use our user-defined comparator as well to extend the usage of the **includes()** function.

我们还可以使用用户定义的比较器来扩展**include()**函数的用法。

The syntax for include will be:

include的语法为：

bool includes(
        InputIterator1 first1, 
        InputIterator1 last1,
        InputIterator2 first2, 
        InputIterator2 last2, 
        Compare comp );

Where all the arguments are the same as before except the additional argument which is the user-defined comparator function. Two elements a & b are said to be equal *if (!comp(a, b) && !comp(b, a))* is true/

其中所有参数均与以前相同，只是附加参数是用户定义的比较器函数。 *如果(！comp(a，b)&&！comp(b，a))*为true / *，*则认为两个元素a＆b相等*。*

We can show the need for a user-defined comparator through an example.

我们可以通过一个示例说明对用户定义比较器的需求。

Let's say we the elements are not any primitive data type, but rather some user-defined data type. In those cases to compare two objects(elements), we need to write our user-defined comparator.

假设我们的元素不是任何原始数据类型，而是某些用户定义的数据类型。 在这些情况下，要比较两个对象(元素)，我们需要编写我们的用户定义比较器。

Sat for example below is the class structure:

下面的例子是类结构：

class student {
    
        int score;
        int roll;
        string name;
    
    public:
        student()
        {
            score = 0;
            roll = 0;
            name = "";
        }
        student(int sc, int ro, string nm)
        {
            score = sc;
            roll = ro;
            name = nm;
        }
    
        int get_score()
        {
            return score;
        }
        int get_roll()
        {
            return roll;
        }
        string get_name()
        {
            return name;
        }
    };

In the above case, we can’t compare using '<' or '>' operators. Rather we need our user-defined comparator may be something like:

在上述情况下，我们无法使用'<'或'>'运算符进行比较。 相反，我们需要用户定义的比较器可能类似于：

bool comp(student a, student b)
    {
        //if all details are same then both elements are same otherwise false
        if (a.get_name() == b.get_name() && a.get_score() == b.get_score() && a.get_roll() == b.get_roll())
            return false;
    
        return true;
    }

Now you must be wondering why we returned false when all details match. This is because both objects a & b are considered to be same *if !comp(a,b) && !comp(b,a)*. Now can extend the logic as per your use cases.

现在，您一定想知道为什么当所有详细信息匹配时我们返回false。 这是因为*如果！comp(a，b)&&！comp(b，a)*认为两个对象a和b相同。 现在可以根据您的用例扩展逻辑。

> 翻译自: [https://www.includehelp.com/stl/std-includes-function-with-example.aspx][https_www.includehelp.com_stl_std-includes-function-with-example.aspx]

[https_www.includehelp.com_stl_std-includes-function-with-example.aspx]: https://www.includehelp.com/stl/std-includes-function-with-example.aspx