std::find_if_std :: find_first_of（）与C ++中的示例

系统管理员 2023-03-05 15:50 3阅读 0赞

std::find\_if

## std :: find\_first\_of()作为STL函数 **(**std::find\_first\_of() as a STL function**)** ##

**find\_first\_of()** in a useful STL function, which is invoked by a string and searches the first position of any character out of the character list provided(string str) in the argument.

**find\_first\_of()**在有用的STL函数中，该函数由字符串调用，并从参数中提供的字符列表(字符串str)中搜索任何字符的第一位置。

**Syntax:**

**句法：**

size_t find_first_of (const string& str, size_t pos = 0) const;

Where,

哪里，

*  const string& str \- collection of characters any of which needs to be searched.
    
    const string＆str-需要搜索任何字符的集合。
 *  size\_t pos \- an optional parameter which is passed with a default value of 0. Position defines the start index of the invoking string from where searching should start.
    
    size\_t pos-一个可选参数，默认值为0传递。position定义了从开始搜索的位置开始的调用字符串的起始索引。

**Return type:** size\_t

**返回类型：** size\_t

It returns the index if it finds any character of the mentioned collection in the invoking string. If none of the characters is present in the invoking string then it returns a *string::npos*.

如果在调用字符串中找到所提及集合的任何字符，则返回索引。 如果调用字符串中没有字符，则返回*string :: npos* 。

It returns the index immediately if any of the characters found.

如果找到任何字符，它将立即返回索引。

**Example 1:** Position argument not passed, so by default it's 0

**示例1：**未传递位置参数，因此默认为0

#include <bits/stdc++.h>
    using namespace std;
    
    int main()
    {
        string str = "includehelp";
    
        string re = "aeiou";
        //its searching in the string str
        //it searches any character from the string re
        //now if any character of re is found then it simply 
        //returns the position of the character found
    
        cout << "the first vowel appearing in the string: " << str << " is " << str[str.find_first_of(re)] << endl;
    
        return 0;
    }

**Output:**

**输出：**

the first vowel appearing in the string: includehelp is i

In the above program, 
    In the first case,
    The invoking string is str, "includehelp"
    The collection of characters which are being searched 
    "aeiou" -> 'a', 'e', 'i', 'o', 'u'
    
    The position argument is not passed so 
    it will start searching from position 0 which is 'i', 
    since 'i' falls in the collection of characters thus it returns 0

**Example 2:** Position argument is passed

**示例2：**传递位置参数

#include <bits/stdc++.h>
    using namespace std;
    
    int main()
    {
        string str = "includehelp";
    
        string re = "aeiou";
        //its searching in the string str
        //it searches any character from the string re
        //now if any character of re is found then it simply 
        //returns the position of the character found
    
        //now this will start searching in str from position=1
        //thus it skips the fisrt vowel 'i'
        cout << "the second vowel appearing in the string: " << str << " is " << str[str.find_first_of(re, 1)] << endl;
    
        return 0;
    }

**Output:**

**输出：**

the second vowel appearing in the string: includehelp is u

In the above case, the starting position is 1 thus it starts searching only from index 1 skipping the first index(0) which is *'i'*. Thus, the first character out of the collection which is found is *'u'*.

在上述情况下，起始位置为1，因此它仅从索引1开始搜索，而跳过了第一索引(0) *'i'* 。 因此，从集合中找到的第一个字符是*'u'* 。

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

std::find\_if

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