C++11のshared pointerの振る舞いを調べるコード。
２つのベクターに代入してリファレンスカウントを出力する、

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

using namespace std;

class X{
    int x;
public:
    X(int x):x(x){
        cout << "constructed" << endl;
    };
    ~X(){
        cout << x << " destructed" << endl;
    }
};

vector< shared_ptr<X>> globalVect;


void add(shared_ptr<X> &x){
    cout << "passed to func" << endl;
    cout << "count " << x.use_count() << endl; // 1
    
    vector< shared_ptr<X>> localVect1;

    localVect1.push_back(x);
    cout << "copy to local vector" << endl;
    cout << "count " << x.use_count() << endl; //2
    
    globalVect.push_back(x);
    cout << "copy to global vector" << endl;
    cout << "count " << x.use_count() << endl; // 3

}

int main(int argc, const char * argv[]) {
    auto x = shared_ptr<X>(new X(10));
    cout << "shared point created" << endl;
    cout << "count " << x.use_count() << endl; // 1
    add(x);
    
    cout << "return to main" << endl;
    cout << "count " << x.use_count() << endl; // 2
    
    globalVect.erase(globalVect.begin(), globalVect.end());
    cout << "deleted from glibal vector" << endl;
    cout << "count " << x.use_count() << endl; // 1
    
    x.reset();
    cout << "manually realeased" << endl;
    cout << "count " << x.use_count() << endl; // 1

    return 0;
}