Runtime error when push_back to a vector

Question

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

int main() {
    vector<pair<int, int>*> *v;
    pair<int, int> *x = new pair<int, int>();
    cin >> x->first >> x->second;
    v->push_back(x);
    cout << v->size() << endl;
    return 0;
}

Why does this code get run-time error? I dont understand. All I do is appending a pair pointer to a vector of pair pointer.

I don't do much C++, but I don't think v is initialised, because it's a pointer the object isn't created implicitly. vector<pair<int, int>*> *v = new vector<pair<int, int>*>(); should work. This would explain why you're getting a segfault - you're trying to access a null pointer v. — Will Richardson
– Will Richardson, Commented Aug 15, 2018 at 5:29
... shit, basic mistake. Im so dump. Yea me too, Im kind switching to js which is more free to create a new object without initiallizing. — Brian Tran
– Brian Tran, Commented Aug 15, 2018 at 5:43

Amit G. · Accepted Answer · 2018-08-15 09:17:17Z

1

First of all: Vector definition should be (this resolves the run-time error):

vector<pair<int, int>*> v;

Second, you don't release the memory of the new pair. This will solve that issue too:

vector<pair<int, int>> v;
pair<int, int> x{ 0,0 };

A vector of pairs, rather than a vector of pair-pointers. On the other hand: If it necessary to use a vector of pointers, smart pointers is a better choice.

edited Aug 15, 2018 at 9:17

answered Aug 15, 2018 at 5:41

Amit G.

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Brian Tran Over a year ago

Im so dump. Thank you.

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