substr有2种用法:
假设:string s = “0123456789”;
string sub1 = s.substr(4); //只有一个数字4表示从下标为4开始一直到结尾:sub1 = “456789”
string sub2 = s.substr(4, 3); //从下标为4开始截取长度为3位:sub2 = “456”
substr有2种用法:
假设:string s = “0123456789”;
string sub1 = s.substr(4); //只有一个数字4表示从下标为4开始一直到结尾:sub1 = “456789”
string sub2 = s.substr(4, 3); //从下标为4开始截取长度为3位:sub2 = “456”