1 //() 可以换成 { }，都一样
 2 int main () {
 3    std::string s0 ("initial string"); 
 4    std::string s1;
 5    std::string s2 (s0);
 6    std::string s3 (s0, 8, 3); //从s0的第八个字符开始，长度是3
 7    std::string s4 ("A character sequence", 6); //截取前六个字符来初始化s4
 8    std::string s5 ("Another character sequence");
 9    std::string s6a (10, ‘x‘);//10个字符x
10    std::string s6b (10, 42);//10个字符*，因为x对应的asic码是42
11    std::string s7 (s0.begin(), s0.begin()+7);//s0的前7个字符，第二个参数要么是end，要么就是从begin开始加上长度
12    std::cout << "s1: " << s1 << "\ns2: " << s2 << "\ns3: " << s3;
13    std::cout << "\ns4: " << s4 << "\ns5: " << s5 << "\ns6a: " << s6a;
14    std::cout << "\ns6b: " << s6b << "\ns7: " << s7 << ‘\n‘;
15    return 0;
16 }
17 输出：
18 s1:
19 s2: initial string
20 s3: str
21 s4: A char
22 s5: Another character sequence
23 s6a: xxxxxxxxxx
24 s6b: **********
25 s7: initial