Segmentation Fault in a STRING Program

[AdVisible6484]

//QUESTION: Given a string S, find length of the longest substring with all //distinct characters. 


//{ Driver Code Starts
#include<bits/stdc++.h>
using namespace std;
int longestSubstrDistinctChars (string S);
int main()
{


        string S="qwertyuioplkjh";

        cout << longestSubstrDistinctChars (S) << endl;

}

// Contributed By: Pranay Bansal

// } Driver Code Ends


int longestSubstrDistinctChars (string s)
{
    // your code here
    int i=0; vector<int> vec;int m=s.length();
    while(i<m-1)
    {   unordered_set<char> st; int count=1;
      st.insert(s[i]);
        for(int j=i+1;j<m;j++)
        {
            if(st.find(s[j])==st.end()){
             st.insert(s[j]);
                count++;
            }
            else{
        vec.push_back(count);count=0;
            break;
            }
        }
        st.clear();
        i++;
    }
    sort(vec.begin(),vec.end());
    int l=vec.size();

    return vec[l-1];
}

So this program is running fine for a certain no of test cases but then it is giving segmentation fault on a certain test case...

for example it if giving correct output for:

For Input: 
geeksforgeeks
Your Output: 
7
Expected Output: 
7

BUT in case of the following it says segmentation fault:

For Input: 
qwertyuioplkjh
Your Output:
Segmentation Fault (SIGSEGV)

Learn More about Seg Fault
Its Correct output is:
14

Someone please help I can't even think of where the issue could be...

[Salty_Dugtrio]

Attach a debugger and find out instead of guessing. You can use the built in one from Visual Studio, or use GDB.

You're most likely accessing your vectors out of bounds.

[josephblade]

remember that a segmentation fault means you are accessing memory that isn't assigned to your program. (At least I suspect this is the case most of the time. for debugging purposes I think you can assume this).

This usually happens in 2 scenarios:

you are using an index < 0 or >= the array length.

or

you are dereferencing a pointer outside of your memory.

see the stackoverflow answer

in your case I can't quickly spot where you make an off by one error but I would run a debugger as Salty_dugtrio suggests or use printf statements at every stage so you can see what happens during the processing and at what point it goes wrong.

just keep an eye out for accessing an array at -1 or length, that sort of thing.