C++ std::find_first_of()用法及代碼示例

std::find_first_of() 作為 STL 函數

find_first_of() 在一個有用的 STL 函數中，它由字符串調用，並從參數中提供的字符列表(字符串 str)中搜索任何字符的第一個位置。

用法:

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

其中，

• const string& str- 需要搜索的任何字符的集合。
• size_t pos- 一個可選參數，默認值為 0。Position 定義調用字符串的起始索引，從哪裏開始搜索。

返回類型： size_t

如果在調用字符串中找到提到的集合的任何字符，則返回索引。如果調用字符串中不存在任何字符，則它返回一個字符串::npos。

如果找到任何字符，它會立即返回索引。

範例1：未傳遞位置參數，因此默認為 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;
}

輸出：

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

範例2：位置參數被傳遞

#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;
}

輸出：

the second vowel appearing in the string:includehelp is u

在上述情況下，起始位置為 1，因此它僅從索引 1 開始搜索，跳過第一個索引 (0)，即 'i'。因此，找到的集合中的第一個字符是 'u'。