Stack vs Heap C++

https://www.learncpp.com/cpp-tutorial/79-the-stack-and-the-heap/

Heap allocation in C++ is done by using new keyword.

#include <iostream>

#include <vector>

using namespace std;

struct Node {

string tag;

vector<Node *> children;

};

vector<Node *> nodes;

void process(){

for (int i = 0; i< 3; i++){

Node* n = new Node() ;

n->tag = "a";

nodes.push_back(n);

}

}

int main() {

std::cout << "Hello World!\n";

process();

for (int i = 0; i< 3; i++){

cout<<nodes[i]->tag<<endl;

}

}

above works fine but below will not

#include <iostream>

#include <vector>

using namespace std;

struct Node {

string tag;

vector<Node *> children;

};

vector<Node *> nodes;

void process(){

for (int i = 0; i< 3; i++){

Node n ; // n is allowed on stack and might be deallocated by OS

n.tag = "a";

nodes.push_back(&n);

}

}

int main() {

std::cout << "Hello World!\n";

process();

for (int i = 0; i< 3; i++){

cout<<nodes[i]->tag<<endl; // this will cause segmentation fault

}

}