subtle_bug.cpp

#include <iostream>
#include <vector>
#include <string>

int main(int argc, char *argv[]) {
    std::vector<int> bob(1);
    bob.push_back(20);
    bob.push_back(bob[0]);
    for (auto it = bob.begin();
         it != bob.end();
         ++it) {
        std::cout << *it << "\n";
    }
    return 0;
}