make-shared

(Using Visual Studio 2010) I'm trying to create a shared_ptr of an existing class in my project (class was written a decade before std::shared_ptr existed). This class takes a non-const pointer to another object, it's empty parameter constructor is private. class Foobar { public: Foobar(Baz* rBaz); private: Foobar(); } When I try to create a shared_ptr to it, things don't go well: Baz* myBaz = new Baz(); std::shared_ptr<Foobar> sharedFoo = std::make_shared<Foobar>(new Foobar(myBaz)); On VS2010, this gives me error C2664: 'Foobar::Foobar(const Foobar &)' : cannot convert parameter 1 from

I'm interested if these two lines of code are the same: shared_ptr<int> sp(new int(1)); // double allocation? shared_ptr<int> sp(make_shared<int>(1)); // just one allocation? If this is true could someone please explain why is it only one allocation in the second line? The first case does not perform a double allocation, it performs two allocations, one for the managed object and one for the control block of the shared_ptr . For the second case, cppreference has a good explanation for why std::make_shared usually only performs one memory allocation it says ( emphasis mine going forward ): This

When initializing a shared_ptr member variable: // .h class Customer { public: Customer(); private: std::shared_ptr<OtherClass> something_; } // .cpp Customer(): something_(new OtherClass()) { } vs. Customer(): something_(std::make_shared<OtherClass>()) { } Is the make_shared version allowed? I always seem to see the first version, which is preferred? The only times when make_shared is not allowed are: If you're getting a naked pointer allocated by someone else and storing it in shared_ptr . This is often the case when interfacing with C APIs. If the constructor you want to call is not public

I was experimenting with shared_ptr and make_shared from C++11 and programmed a little toy example to see what is actually happening when calling make_shared . As infrastructure I was using llvm/clang 3.0 along with the llvm std c++ library within XCode4. class Object { public: Object(const string& str) { cout << "Constructor " << str << endl; } Object() { cout << "Default constructor" << endl; } ~Object() { cout << "Destructor" << endl; } Object(const Object& rhs) { cout << "Copy constructor..." << endl; } }; void make_shared_example() { cout << "Create smart_ptr using make_shared..." << endl