C++ works fine at my computer but gets address sanitizer heap-buffer-overflow errors on leetcode

Question

I was trying to solve leetcode problem "929. Unique Email Addresses", the code works fine at my computer on Visual Studio Code but when I pasted it on the leetcode, I got address sanitizer heap-buffer-overflow error. The code is shown below:

class Solution {
 public:
  int numUniqueEmails(vector<string>& emails) {
    string::iterator it;
    for (int i = 0; i < emails.size(); i++) {
      for (it = emails[i].begin(); *it != '@'; it++) {
        if (*it == '.') {
          emails[i].erase(it);
          it--;
        }
        if (*it == '+') {
          while (*it != '@') {
            emails[i].erase(it);
          }
          break;
        }
      }
      sort(emails.begin(), emails.end());
      for (int j = 0; j < emails.size(); j++) {
        if (emails[j] == emails[j + 1]) {
          emails.erase(emails.begin() + j);
          j--;
        }
      }
    }
    return emails.size();
  }
};

Can someone let me know why the error occurs?

Answer 1

Because the following loops:

for (it = emails[i].begin(); *it != '@'; it++)
   ...

and

while (*it != '@')
  ...

iterate with it over the string without never ever verifying if the end of the string was reached. If you have a single ill-formatted email address in the input data, you therefore go out of bounds. So UB.

In addition, you also go out of bounds here:

 for (int j = 0; j < emails.size(); j++) {
    if (emails[j] == emails[j + 1]) {  // what when j == size-1 ????

Finally a potentially nasty issue as well (but could affect the result): your first for loop should end before the sort() . Why? because with some bad luck, the sorting will change the order of the elements, causing an unprocessed address to move before the current i index and thus remain unprocessed.

Demo with some additional display of intermediary results and some extreme cases.