(newbie need help) Problem with template vectors

[Manuel]

Hi!
This is a simple exercise with vectors. I must insert an element as
second item.

This work:

-------------------------------
#include <iostream>
#include <vector>
using namespace std;

int main() {
vector<int> storage;
storage.push_back(10);
storage.push_back(20);
storage.push_back(30);
storage.push_back(40);
storage.push_back(50);
vector<int>::iterator iter = storage.begin();

storage.insert(iter + 2, 15);

while (iter != storage.end()) {
cout << *iter << endl;
iter++;
}
}
-------------------------------


This crash!!

-------------------------------
#include <iostream>
#include <vector>
using namespace std;

int main() {
vector<int> storage;
storage.push_back(10);
storage.push_back(20);
storage.push_back(30);
storage.push_back(40);
//storage.push_back(50);
vector<int>::iterator iter = storage.begin();

storage.insert(iter + 2, 15);

while (iter != storage.end()) {
cout << *iter << endl;
iter++;
}
}

 

[Peteris Krumins]

Hi!
This is a simple exercise with vectors. I must insert an element as
second item.

This work:

-------------------------------
#include <iostream>
#include <vector>
using namespace std;

int main() {
vector<int> storage;
storage.push_back(10);
storage.push_back(20);
storage.push_back(30);
storage.push_back(40);
storage.push_back(50);
vector<int>::iterator iter = storage.begin();

storage.insert(iter + 2, 15);

while (iter != storage.end()) {
cout << *iter << endl;
iter++;
}
}

Because by inserting an element into a vector you invalidate the
iterator iter.
After: storage.insert(iter + 2, 15), iterator iter can no longer be
used.

Here is a an example which works:

#include <iostream>
#include <vector>
using namespace std;

int main() {
vector<int> storage;
storage.push_back(10);
storage.push_back(20);
storage.push_back(30);
storage.push_back(40);
storage.push_back(50);

storage.insert(storage.begin() + 2, 15);

vector<int>::iterator iter = storage.begin();
while (iter != storage.end()) {
cout << *iter << endl;
iter++;
}
}


P.Krumins

 

[Manuel]

Because by inserting an element into a vector you invalidate the
iterator iter.
After: storage.insert(iter + 2, 15), iterator iter can no longer be
used.

Thanks, and sorry to boring mailing list with stupid newbie questions...

Ciao!

 

[benben]

Hi!
This is a simple exercise with vectors. I must insert an element as
second item.

This work:

-------------------------------
#include <iostream>
#include <vector>
using namespace std;

int main() {
vector<int> storage;
storage.push_back(10);
storage.push_back(20);
storage.push_back(30);
storage.push_back(40);
storage.push_back(50);
vector<int>::iterator iter = storage.begin();

storage.insert(iter + 2, 15);

while (iter != storage.end()) {
cout << *iter << endl;
iter++;
}
}
-------------------------------


This crash!!

-------------------------------
#include <iostream>
#include <vector>
using namespace std;

int main() {
vector<int> storage;
storage.push_back(10);
storage.push_back(20);
storage.push_back(30);
storage.push_back(40);
//storage.push_back(50);
vector<int>::iterator iter = storage.begin();

storage.insert(iter + 2, 15);

while (iter != storage.end()) {
cout << *iter << endl;
iter++;
}
}
-------------------------------

Why?? In both cases I've storage.size > 2...

THANKS!!!

Merry Christmas!

My guess is that iter is invalidated after the insert call. The first
example worked because you were lucky... To solve the problem, just
reassign storage.begin() to iter after the call to insert but before
using iter in any means:

int main() {
vector<int> storage;
storage.push_back(10);
storage.push_back(20);
storage.push_back(30);
storage.push_back(40);
//storage.push_back(50);

vector<int>::iterator iter = storage.begin();
cout << (iter == storage.begin()) << '\n'; // 1

storage.insert(iter + 2, 15);
cout << (iter == storage.begin()) << '\n'; // 0

iter = storage.begin(); // do this!

while (iter != storage.end()) {
cout << *iter << endl;
iter++;
}
}

Ben

 

[Manuel]

Thanks!
Yes, the problem is iterator.
Regards,

Manuel

 

[E. Mark Ping]

vector<int>::iterator iter = storage.begin();

storage.insert(iter + 2, 15);

This invalidates all iterators in "storage"

while (iter != storage.end()) {
cout << *iter << endl;
iter++;
}

This uses an invalidated iterator.

 

[Manuel]

This uses an invalidated iterator.

Thanks.
Sorry to boring NG with this newbie questions.

Regards,

Manuel