C ++中子字符串方法的问题[重复]

Question

给定字符串 IP 作为输入

int index, i=0;
string substr;
while(i!=-1 && IPv4){
            index=IP.find(".",i+1);
            substr=IP.substr(i,index);
            cout << substr << " found at index " << index << " with i= "<<i << endl;
            i=index;
        }

输入：“172.16.254.1”

预期输出：

172 found at index 3 with i= 0
.16 found at index 6 with i= 3
.254 found at index 10 with i= 6
.1 found at index -1 with i= 10

结果输出：

172 found at index 3 with i= 0
.16.25 found at index 6 with i= 3
.254.1 found at index 10
.1 found at index -1 with i= 10

所以算法使用的值应该是正确的，但我得到了错误的子字符串。

任何意见将不胜感激

Answer 1

substr 采用索引和长度。

另外，将变量命名为与成员函数相同可能不是一个好主意。你可能想要：

ip_chunk = IP.substr(i, index - i);