C++ strange behaviour mutator vector -

i've been working on work school have create client class 4 string, 4 int , vector(int) last argument. problem is, when want print of vector's elements, if use mutator directly, printing nonsence.

vector<int> v_int; vector<int>::iterator it_v_i; v_int.push_back(2); v_int.push_back(3); v_int.push_back(7); v_int.push_back(1);  client client("nom1", "prenom1", "adress1", "city1", "comment1", 1240967102, 44522, 5, 10, v_int);  v_int = client.getidresources(); (it_v_i = v_int.begin(); it_v_i != v_int.end(); it_v_i++) {     cout << *it_v_i << ", "; } 

print 2,3,7,1 expected, following code

for (it_v_i = client.getidresources().begin(); it_v_i != client.getidresources().end(); it_v_i++) {     cout << *it_v_i << ", "; } 

print unidentified number (like 3417664...), unidentified number, 7, 1

i don't understand why happening

edit :

constructor :

client::client(const string& name, const string& surname, const string& adress, const string& city, const string& comment,             const int& phonenb, const int& postalcode, const int& termappointment, const int& priority, const vector<int>& idresources)                 : name(name), surname(surname), adress(adress), city(city), comment(comment), phonenumber(phonenb),                 postalcode(postalcode), termappointment(termappointment), priority(priority), idresources(idresources) 

{ }

mutator :

std::vector<int> getidresources() const{ return idresources; } 

the problem in second snippet two temporary vectors being used obtain begin() , end() iterators (assuming declaration std::vector<int> client.getidresources() , not std::vector<int>& client.getidresources()). means it_v_i referring elements of destructed std::vector. when it_v_i dereferenced causes undefined behaviour.

to make second code snippet function correctly reference std::vector needs returned client.getidresources(). however, returning references internal class members introduces other problems, such lifetime issues.