bug

for (int i = 0; i < task_vec[index].breakCount(); i++) {
    task_vec[index].eraseBreak(i);
}

size_t DayTask::breakCount() const
{
    return break_vec.size();
}

void DayTask::eraseBreak(int index)
{
    break_vec.erase(break_vec.begin() + index);
}

std::vector<Break> DayTask::break_vec;