What could be causing the Segmentation Fault when attempting to print a 2D vector

This is a homework question. I am working on my Hash Table assignment and I ran into some issues when trying to print the table.

Constraints:

• C++11
• No std::map or std::unordered_map

Minimal Reproducible Example

#include <iostream>
#include <vector>
#include <atomic>
#include <ctime>
#include <iomanip>
#include <string>

class DataEntry {
public:
  std::string get_date() { return date; }
  std::string get_country() { return country; }
  int get_c_cases() { return c_cases; }
  int get_c_deaths() { return c_deaths; }
  inline void set_date(std::string set_date) { this->date = set_date;};
  inline void set_country(std::string set_country) { this->country = set_country;};
  inline void set_c_deaths(int set_c_deaths) { this->c_deaths = set_c_deaths;};
  inline void set_c_cases(int set_c_cases) { this->c_cases = set_c_cases;};

private:
  std::string date;
  std::string country;
  int c_cases;
  int c_deaths;
};

class CovidDB {
private:
  std::vector<std::vector<DataEntry*>> HashTable;
  int size = 17;

public:
  void display_table();
  bool add(DataEntry* entry);
  int hash(std::string country);
};

int CovidDB::hash(std::string country) {
  int sum = 0;
  int count = 0;
  
  for (char c : country) {
    sum = sum + ((count + 1) * c);
    count++;
  }
  return sum % size; //returns the hash
}

void CovidDB::display_table() {
  for (const auto& vec : HashTable) {
    for (const auto& entry : vec) {
      if (entry != nullptr) {
        std::cout << "[Date: " << entry->get_date() << "], "
                  << "[Country: " << entry->get_country() << "], "
                  << "[Cases: " << entry->get_c_cases() << "], "
                  << "[Deaths: " << entry->get_c_deaths() << "]" << std::endl;
      }
    }
  }
}

bool CovidDB::add(DataEntry* entry) {
  time_t now = time(0);
  tm* ltm = localtime(&now);
  // DATE FORMAT: mm/dd/yy
  std::string current_date_str = std::to_string(1 + ltm->tm_mon) + "/" + std::to_string(ltm->tm_mday) + "/" + std::to_string(ltm->tm_year % 100);
  std::istringstream iss(current_date_str);
  std::tm current_date = {};
  iss >> std::get_time(&current_date, "%m/%d/%y");
  
  std::tm entry_date = {};
  std::istringstream iss2(entry -> get_date());
  iss2 >> std::get_time(&entry_date, "%m/%d/%y");
  
  if (mktime(&current_date) > mktime(&entry_date)) {
    std::cout << "[Record rejected]" << std::endl;   
    return false;
  }
  
  int index = hash(entry -> get_country());
  
  if (HashTable[index].empty()) {
    HashTable[index].push_back((entry));
  } else {
    bool added = false;
    for (DataEntry* existing_entry : HashTable[index]) {

      std::atomic<bool> valid(false);
      valid.store(hash(existing_entry->get_country()) == hash(entry->get_country()) &&
                       existing_entry->get_country() == entry->get_country());
      if (valid) {
        existing_entry->set_date(entry -> get_date());
        existing_entry->set_c_cases(existing_entry->get_c_cases() + entry->get_c_cases());
        existing_entry->set_c_deaths(existing_entry->get_c_deaths() + entry->get_c_deaths());
        added = true;
        delete entry;
        break;
      }
    }
    if (!added) {
      HashTable[index].push_back(entry);
    }
  }
  return true;
  return true;
}

int main() {
  CovidDB db;

  // Create two DataEntry objects
  DataEntry* entry1 = new DataEntry();
  entry1->set_date("01/01/23");
  entry1->set_country("Slovenia");
  entry1->set_c_cases(1);
  entry1->set_c_deaths(1);

  DataEntry* entry2 = new DataEntry();
  entry2->set_date("02/02/23");
  entry2->set_country("Slovenia");
  entry2->set_c_cases(1);
  entry2->set_c_deaths(1);

  // Add the entries to the CovidDB
  db.add(entry1);
  db.add(entry2);

  // Display the table
  db.display_table();

  // Clean up memory
  delete entry1;
  delete entry2;

  return 0;
}

The print function seems to work fine for 80% of the time (estimate), for instance when I am pushing data from .csv file into the 2D vector and print it works fine, but when I try to group 2 entries of the same hash

eg:

Country: Slovenia
Date: 01/01/23
Cases: 1
Deaths: 1

Country: Slovenia
Date: 02/02/23
Cases: 1
Deaths: 1

It segfaults...I am aware that SEGFAULT means one is trying to access memory that doesn't belong to him (usually trying to deref a nullptr)

I tried loads of stuff before asking a question here:

Rubber duck Debugging

I noticed that the outer loop runs hash-1 times by putting std::court << "here"; in-between the loops, which means that something goes wrong when it comes to the index of the entry.

I also changed auto to std::vecotr<DataEntry*> vec and to DataEntry* since the outer vector is a vector of vectors and the inner vectors are vectors of DataEntry pointers.

Debugging

I tried debugging the executable with gbd, since I can't configure my Vs Code debugger, but it throws an error

Missing separate debuginfos, use: yum debuginfo-install glibc-2.28-211.el8.x86_64 libgcc-8.5.0-16.el8_7.x86_64 libstdc++-8.5.0-16.el8_7.x86_64

I googled it and the only solution I found was to root install these libraries, which I can't, since this is the school's server and running sudo will get me kicked off.

I tried the XCode debugger but for some reason my code there runs differently...Could it be because the ssh is Linux and the other one isn't?

Guards

I added "guards" to prevent printing an empty hash table, and a guard so that I'm not de-referencing a nullptr, unfortunately, had no effect.