c++中std::find_std :: find（）与C ++中的示例

比眉伴天荒 2023-03-05 11:57 7阅读 0赞

c++中std::find

## find()作为STL函数 **(**find() as a STL function**)** ##

**find()** is an STL function that comes under the <*algorithm>* header file which returns an iterator to the first occurrence of the searching element within a range.

**find()**是STL函数，位于< *algorithm>*头文件下面，该文件将迭代器返回到范围内搜索元素的第一个匹配项。

**Syntax:**

**句法：**

InputIterator find(
        InputIterator first, 
        InputIterator last, 
        const T& val);

Where,

哪里，

*  InputIterator first \- iterator to start of the searching range
    
    首先使用InputIterator-迭代器开始搜索范围
 *  InputIterator last \- iterator to end of the searching range
    
    InputIterator last-迭代到搜索范围的结尾
 *  const T& val \- value to be searched of datatype T
    
    const T＆val-要搜索的数据类型T的值

**What is InputIterator?**  
Iterator to first position of the range where we find the searching element. If searching element is not found it returns iterator to the end

**什么是InputIterator？**  
迭代到找到搜索元素的范围的第一个位置。 如果未找到搜索元素，则将迭代器返回到末尾

**Return type:** bool

**返回类型：** bool

Using the above syntax the elements in the corresponding ranges are searched whether the searching element is found.

使用以上语法，搜索相应范围内的元素是否找到了搜索元素。

**Time complexity:** Linear time, O(n)

**时间复杂度：**线性时间，O(n)

**Difference between [binary\_search()][binary_search] and find() functions**

**[binary\_search()][binary_search]和find()函数之间的[区别][binary_search]**

*  std::binary\_search() function returns Boolean telling whether it finds or not. It doesn't return the position. But, std::find() searches the position too. It returns an iterator to the first position.
    
    std :: binary\_search()函数返回布尔值，指示是否找到。 它不返回位置。 但是，std :: find()也会搜索位置。 它将迭代器返回到第一个位置。
 *  std::binary\_search() searches in O(logn) time whether std::find() searches in linear time.
    
    std :: binary\_search()以O(logn)时间进行搜索，无论std :: find()以线性时间进行搜索。

**Example 1:** When the searched element is found and have only one instance in the searching range

**示例1：**当找到被搜索元素并且在搜索范围内只有一个实例时

#include <bits/stdc++.h>
    using namespace std;
    
    int main()
    {
        vector<int> arr{ 1, 2, 3, 8, 4, 3 };
    
        int searching_element = 8;
        vector<int>::iterator it;
        //starting iterator of range= arr.begin()
        //end iterator of range =arr.end()
    
        it = find(arr.begin(), arr.end(), searching_element);
        if (it != arr.end())
            cout << searching_element << " is at position: " << it - arr.begin() << endl;
        else
            cout << searching_element << "not found";
    
        return 0;
    }

**Output:**

**输出：**

8 is at position: 3

In the above program, we have checked the searching element and we found it at 3rd index(0-indexing)

在上面的程序中，我们检查了搜索元素，并在第三个索引(0索引)处找到了它

**Example 2:** When the searched element is found and have more than one instance in the searching range

**示例2：**找到搜索到的元素并且在搜索范围内有多个实例

#include <bits/stdc++.h>
    using namespace std;
    
    int main()
    {
        vector<int> arr{ 1, 2, 3, 8, 4, 3 };
    
        int searching_element = 3;
        vector<int>::iterator it;
        //starting iterator of range= arr.begin()
        //end iterator of range =arr.end()
    
        it = find(arr.begin(), arr.end(), searching_element);
        if (it != arr.end())
            cout << searching_element << " is at position: " << it - arr.begin() << endl;
        else
            cout << searching_element << "not found";
    
        return 0;
    }

**Output:**

**输出：**

3 is at position: 2

In the above case, we are searching 3 in the array which has two instances one at position index 2 and the other is at position 5. Since **std::find()** stops searching whenever it finds the searching element thus it returns index 2 (Check how we found the position from the iterator it returned).

在上述情况下，我们在数组中搜索3，该数组在位置索引2上有两个实例，另一个在位置5上。由于**std :: find()**每当找到搜索元素时就停止搜索，因此返回索引2(检查我们如何从返回的迭代器中找到位置。

**Example 3:** When the searched element is not found in the searching range

**示例3：**在搜索范围内未找到搜索元素时

#include <bits/stdc++.h>
    using namespace std;
    
    int main()
    {
        vector<int> arr{ 1, 2, 3, 8, 4, 3 };
    
        int searching_element = 7;
        vector<int>::iterator it;
        //starting iterator of range= arr.begin()
        //end iterator of range =arr.end()
     
        it = find(arr.begin(), arr.end(), searching_element);
        if (it != arr.end())
            cout << searching_element << " is at position: " << it - arr.begin() << endl;
        else
            cout << searching_element << " not found";
    
        return 0;
    }

**Output:**

**输出：**

7 not found

In the above case, the searching element is not present and that's why it returned *arr.end()* which means iterator to the end of the range.

在上述情况下，不存在*search*元素，这就是为什么它返回*arr.end()*的原因，这意味着迭代器将到达范围的末尾。

> 翻译自: [https://www.includehelp.com/stl/std-find-with-examples-in-cpp.aspx][https_www.includehelp.com_stl_std-find-with-examples-in-cpp.aspx]

c++中std::find

[binary_search]: https://www.includehelp.com/stl/std-binary_search-in-cpp.aspx
[https_www.includehelp.com_stl_std-find-with-examples-in-cpp.aspx]: https://www.includehelp.com/stl/std-find-with-examples-in-cpp.aspx