std::shared_ptr<std::string> test() {
return std::make_shared<std::string>("sdsd");
}
cout << *test() << endl;
The above code works. Can someone please let me know where is the "sdsd" string stored. I was expecting it to error out as rvalue is a temporary object. Where is the rvalue copied to and stored in?
With weak_ptr
std::weak_ptr<std::string> test() {
return std::make_shared<std::string>("sdsd");
}
cout << *test().lock() << endl;
Interestingly the above code errors out. What's the difference?
In
std::shared_ptr<std::string> test() {
return std::make_shared<std::string>("sdsd");
}
the constructed shared_ptr is returned and lives on as a temporary variable long enough to be used by the caller before going out of scope and freeing the string allocated by make_shared.
The "sdsd" string is stored in dynamic storage owned by the returned shared_ptr.
In
std::weak_ptr<std::string> test() {
return std::make_shared<std::string>("sdsd");
}
the shared_ptr wasn't returned and went out of scope, taking the string allocated by make_shared with it. Since this was the only existing copy of the shared_ptr this leaves the returned temporary weak_ptr variable connected to an expired share_ptr. If you test the return value of lock you'll see it's a default-constructed shared_ptr holding a null pointer.
Documentation for std::weak_ptr::lock.
The "sdsd" string isn't stored anywhere after test returns. It departed when the shared_ptr that owned it went out of scope.