Vector of smart pointers destructor call

Question

Why does the Node destructor get called only once instead of 5 times in the code below?

#include <iostream>
#include <vector>
#include <memory>

struct Node {
    ~Node() {std::cout << "Node destructor called.\n";}
};

void foo() {
    std::vector<std::shared_ptr<Node>> nodes(5, std::make_shared<Node>());
}

int main() {
    foo();
    std::cout << "foo() ended.\n";
}

Answer 1

Your vector contains five copies of the original shared pointer, all sharing ownership of the one single pointee .

To create five separate objects, each owned by one shared pointer, write it like this:

std::vector<std::shared_ptr<Node>> nodes;
for (int i = 0; i != 5; ++i) nodes.push_back(std::make_shared<Node>());

Answer 2

Kerrek SB explained the situation well, but to do what you want to do in a different way, you could also the std::generate_n algorithm:

std::vector<std::shared_ptr<Node>> nodes;
std::generate_n(
    std::back_inserter(nodes),
    5,
    std::make_shared<Node>);

This is more along the lines of what you thought you were doing originally.

Or, similarly:

std::vector<std::shared_ptr<Node>> nodes(5);
std::generate(nodes.begin(), nodes.end(), std::make_shared<Node>);