Issues with the substring method in C++

Question

Given the string IP as input

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;
        }

Input: "172.16.254.1"

Expected output:

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

Resulting output:

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

So the values the algorithm uses should be correct and yet I get the wrong substring.

Any input would be appreciated

Answer 1

substr takes an index and a length.

Also, it's probably not a good idea to name your variable the same as a member function. You probably want:

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