string::find_first_of

string (1)	size_t find_first_of (const string& str, size_t pos = 0) const noexcept;
c-string (2)	size_t find_first_of (const char* s, size_t pos = 0) const;
buffer (3)	size_t find_first_of (const char* s, size_t pos, size_t n) const;
character (4)	size_t find_first_of (char c, size_t pos = 0) const noexcept;

功能：在后面的字符串中查找前面string的每个字符

#include <iostream>
#include <string>
using namespace std;

int main()
{
string s1("abcdef");
string s2("dgte");
size_t n = s1.find_first_of(s2);
cout << n << endl;
n = s1.find_first_of(s2, 4);
cout << n << endl;
const char *s3 = "hijfkmn";
n = s1.find_first_of(s3);
cout << n << endl;
n = s1.find_first_of(s3, 3, 4); //s3的前4个字符中查找从s1的位置3开始的字符
cout << n << endl;
n = s1.find_first_of('c',3);//从s1的位置3(第4个)开始查找‘c’
cout << n << endl;
return 0;
}