unique-ptr

问题 Given a base class for multiple derived class, the goal was to create a wrapper class that allowed an STL container to see objects with the base interface, event though different derived classes may actually be added to the container. (See Retrieve data from heterogeneous std::list). After some tinkering, I came up with a new derived class that was a wrapper around a unique_ptr to the base class. However, the move constructor has me confused. class Base { friend class BaseWrapper; virtual

问题 I have two sets and an iterator to an element of a : set<unique_ptr<X>> a, b; set<unique_ptr<X>>::iterator iter = find something in a; I would like to remove the element pointed by iter from a and insert it into b . Is it possible? How? 回答1: Well, I suspect there is no normal way to do it. But there is always a non-normal one :) You can do the following: auto tmp = const_cast<std::unique_ptr<std::string>&&>(*iter); a.erase(iter); b.insert(std::move(tmp)); Ok, the very first line violated set

问题 I have two sets and an iterator to an element of a : set<unique_ptr<X>> a, b; set<unique_ptr<X>>::iterator iter = find something in a; I would like to remove the element pointed by iter from a and insert it into b . Is it possible? How? 回答1: Well, I suspect there is no normal way to do it. But there is always a non-normal one :) You can do the following: auto tmp = const_cast<std::unique_ptr<std::string>&&>(*iter); a.erase(iter); b.insert(std::move(tmp)); Ok, the very first line violated set

问题 Can somebody tell me, what is wrong with the following initialization of unique_ptr? int main() { unique_ptr<int> py(nullptr); py = new int; .... } g++ -O2 xxx.cc -lm -o xxx -std=c++11 says: error: no match for ‘operator=’ (operand types are ‘std::unique_ptr<int>’ and ‘int*’) py = new int; ^ Doing unique_ptr<int> px(new int); works just fine. 回答1: The initialization is fine in both pieces of code, unique_ptr has constructors for both nullptr and naked pointers. What is failing in the first

问题 I'm currently trying to store a std::unique_ptr in a std::unordered_map, but I get a weird compile error. Relevant code: #pragma once #include "Entity.h" #include <map> #include <memory> class EntityManager { private: typedef std::unique_ptr<Entity> EntityPtr; typedef std::map<int, EntityPtr> EntityMap; EntityMap map; public: /* Adds an Entity */ void addEntity(EntityPtr); /* Removes an Entity by its ID */ void removeEntity(int id) { map.erase(id); } Entity& getById(int id) { return *map[id];

问题 I have a base class and its subclass: class Base { public: virtual void hi() { cout << "hi" << endl; } }; class Derived : public Base { public: void hi() override { cout << "derived hi" << endl; } }; Trying to create a helper function that creates a unique pointer of a Derived object. 1) This one works: std::unique_ptr<Base> GetDerived() { return std::make_unique<Derived>(); } 2) But, this one fails to compile: std::unique_ptr<Base> GetDerived2() { auto a = std::make_unique<Derived>(); return

问题 Code: #include <memory> using namespace std; struct T {}; T* foo() { return new T; } T const* bar() { return foo(); } int main() { unique_ptr< T const > p1( bar() ); // OK unique_ptr< T const [] > a1( bar() ); // OK unique_ptr< T const > p2( foo() ); // OK unique_ptr< T const [] > a2( foo() ); // ? this is line #15 } Example errors with Visual C++ 10.0 and MinGW g++ 4.4.1: [d:\dev\test] > cl foo.cpp foo.cpp foo.cpp(15) : error C2248: 'std::unique_ptr<_Ty>::unique_ptr' : cannot access private

问题 Code: #include <memory> using namespace std; struct T {}; T* foo() { return new T; } T const* bar() { return foo(); } int main() { unique_ptr< T const > p1( bar() ); // OK unique_ptr< T const [] > a1( bar() ); // OK unique_ptr< T const > p2( foo() ); // OK unique_ptr< T const [] > a2( foo() ); // ? this is line #15 } Example errors with Visual C++ 10.0 and MinGW g++ 4.4.1: [d:\dev\test] > cl foo.cpp foo.cpp foo.cpp(15) : error C2248: 'std::unique_ptr<_Ty>::unique_ptr' : cannot access private

问题 I created a generic deleter template that can be used to create unique_ptr<>() sub-types allowing for a Deleter other than just delete ptr . It works great with the default optimization flags (i.e. -O0 ), however, when I use -O3 the T & operator * () function, somehow, returns 0 instead of the f_pointer contents. I would like to make sure that we agree that there is something wrong in the compiler and that my template is correct. The following is a complete piece of code that should compile

问题 I haven't yet seen a pimpl example that utilizes both unique_ptr and move-semantics. I want to add a CHelper class to STL derived containers and use pimpl to hide what CHelper does. Does this look right? Derived.h class CDerived : public set<CSomeSharedPtr>, public CHelper { //... }; ` Helper.h // derived containers need to support both copy and move, so CHelper does too class CHelper { private: class impl; unique_ptr<impl> pimpl; public: //--- default: need both cotr & cotr (complete class)