访问shared_ptr矢量对象的问题

I have a problem with accessing shared_ptr Vector from main. My turnOrder function takes 2 sharedPtr vectors, combines and sorts them and puts the objects to another vector(Units).The problem is, when I test the function using for loops it gives exactly what I want but in the int main(), Units vector seems empty and when I try to access any object it gives this exit code: " exit code -1073741819 (0xC0000005) ".

void turnOrder( std::vector<std::shared_ptr<Monster>> monsters, std::vector<std::shared_ptr<Hero>> heroes,  std::vector<std::shared_ptr<Unit>> Units) {

std::vector<std::shared_ptr<Unit>> units;

units.reserve(8);

units.insert(units.begin(), heroes.begin(), heroes.end());
units.insert(units.end(), monsters.begin(), monsters.end());
//TESTING INITIAL VECTOR

for(int i = 0; i < units.size(); i++){
units[i]->printOut();
}
for (int i = 0; i < units.size(); i++) {
units[i]->findSpeedRate();
}
struct X{

inline bool operator() ( const std::shared_ptr<Unit> obj1, const std::shared_ptr<Unit> obj2){
return(obj1->speedRate > obj2->speedRate);
}
};
std::sort(units.begin(), units.end(), X());

for(int i = 0; i < units.size(); i++){
Units.emplace_back(units[i]);
}

//TESTING ORDERED VECTOR
for(int i = 0; i < Units.size(); i++){
Units[i]->printOut();
  }

}


int main(){

std::vector<std::shared_ptr<Unit>> Units;
std::vector<std::shared_ptr<Monster>> monsters;
std::vector<std::shared_ptr<Hero>> heroes;

auto crusader1 = std::make_shared<Crusader>(1);
heroes.emplace_back(crusader1);
/////It goes the same with the other objects(monsters and heroes)

turnOrder(monsters, heroes, Units);
Units[0]->printOut();


}