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>);