C ++ without new and delete

, !

, Align Technology. ++.

, . , ++ . , — .

. new delete. , . , ++ new delete.

, , . , . , .

, , - .


behappy.me

: new delete . , . , .

:

• .
• ,
  
  • c delete;
  • new make-;
  • new .
• .

, new delete STL boost.

new delete?

new delete ++ .

, . , . thread-local , . . storage duration.

, . , , . .

. ( ). :

struct A
{
  std::string str;  //  ,     A (  
                    // ).    -   (*),   
                    //    std::string,       A. 
  // (*)      ,   Small String Optimization  
  //     .
};

void foo()
{
  std::vector<int> v;  //  ,      .
  v.push_back(10);  //   -   (),     
                    // ,        .

  A a;  //    ,      .

  A* pa = new A;  //  pa -  ,      ,
                  //        ,      .
  delete pa;  //    .

  auto upa =  //   upa -  ,      , 
    std::make_unique<A>();  //        ,    
                            //    .
}

, . , . upa->str , .. — *upa. .. / , .

/ , , .. , ^*). a *pa , , — .

++ new, delete. : , ! , . .

, , .

---

^* , / . , .

new delete?

new delete . delete:

• delete ( , memory leak).
• delete ( ).
• delete ( , double delete).
• : delete delete[] ( , undefined behavior).
• delete (dangling pointer).

, .

delete , . new , , , , . , make-.

new delete. , , , new delete.

— .

— , . , , , , .

++ new delete: new[] delete[]. , :

void DoWork(int* buffer, size_t bufSize);

API ^*. , . , .. delete, .

void Call(size_t n)
{
  int* p = new int[n];
  DoWork(p, n);
  delete[] p;  // !
}

, ++ std::vector^**. . , , . :

void Call(size_t n)
{
  std::vector<int> v(n);  // .
  DoWork(v.data(), v.size());
}

, delete, +, .

new delete. . , .

---

^* ++ span<int>. STL- , ( ).

^** ++, , - : «! std::vector (!) , int* — . ! !». ++ Why C++ Sails When the Vasa Sank. , std::unique_ptr<int[]>, dynarray.

, - . , ^*, (. ). .

, - , : , , , - . , , — .

^**, . , , . , .

, , Qt. , . , .. QObject. , , boost::intrusive_ptr.

, . . . , QObject setParent() children() , boost::intrusive_ptr intrusive_ptr_add_ref intrusive_ptr_release .

, , . , , , .

. , , new delete , — .

---

^* : pimpl; (, ).

^** std::locale::facet (. ).

. ++, , .

, , , . . ++ : std::shared_ptr std::unique_ptr. std::weak_ptr, .. std::shared_ptr .

std::auto_ptr, ++ ++17. !

, .. . , std::make_shared std::make_unique, .

.. :

std::unique_ptr<Cookie> cookie(new Cookie(dough, sugar, cinnamon));

:

auto cookie = std::make_unique<Cookie>(dough, sugar, cinnamon);

make- GotW #89 Effective Modern C++, Item 21. , :

• make-:
  
  • .
  • .
• std::make_shared:
  
  • , .. , . We Know Where You Live.

make- , :

• make-:
  
  • deleter. , .. make- new.
  • braced initializer, , perfect forwarding (. Effective Modern C++, Item 30).
• std::make_shared:
  
  • (std::weak_pointer).
  • new delete .
  • (false sharing) (. StackOverflow).

. , delete, make- new. , new, delete.

, make- (a.k.a. STL). Don’t Help the Compiler:

. , (reference counting) - (parent to child relationship).

new delete. - , - .

, . OpenSceneGraph. 3D-, ++ OpenGL.

osg::Referenced, . ref() , unref() , .

osg::ref_ptr<T>, T::ref() T::unref() . boost::intrusive_ptr, ref() unref() .

, OpenSceneGraph 3.0: Beginner's guide:

osg::ref_ptr<osg::Vec3Array> vertices = new osg::Vec3Array;
// ... 
osg::ref_ptr<osg::Vec3Array> normals = new osg::Vec3Array;
// ... 
osg::ref_ptr<osg::Geometry> geom = new osg::Geometry;
geom->setVertexArray(vertices.get());
geom->setNormalArray(normals.get());
// ... 

osg::ref_ptr<T> p = new T. , std::make_unique std::make_shared std::unique_ptr std::shared_ptr, osg::make_ref osg::ref_ptr. , std::make_unique:

namespace osg
{
  template<typename T, typename... Args>
  osg::ref_ptr<T> make_ref(Args&&... args)
  {
    return new T(std::forward<Args>(args)...);
  }
}

:

auto vertices = osg::make_ref<osg::Vec3Array>();  
// ... 
auto normals = osg::make_ref<osg::Vec3Array>();  
// ... 
auto geom = osg::make_ref<osg::Geometry>();
geom->setVertexArray(vertices.get());
geom->setNormalArray(normals.get());
// ... 

. ^*, .

delete osg::Referenced::unref(), new osg::make_ref. new delete.

---

^* , , .

MFC

, MFC. ++ Windows API. GUI Windows.

, Microsoft . .. , , . CDialog::PostNcDestroy(). WM_NCDESTROY — , .

CMainFrame::OnBnClickedCreate() CMyDialog::PostNcDestroy().

void CMainFrame::OnBnClickedCreate()
{
  auto* pDialog = new CMyDialog(this);
  pDialog->ShowWindow(SW_SHOW);
}

class CMyDialog : public CDialog
{
public:
  CMyDialog(CWnd* pParent)
  {
    Create(IDD_MY_DIALOG, pParent);
  }

protected:
  void PostNcDestroy() override
  {
    CDialog::PostNcDestroy();
    delete this;
  }
};

new, delete. — . , PostNcDestroy(), . new, delete, . , .

new delete CModelessDialog CreateModelessDialog, :

class CModelessDialog : public CDialog
{
public:
  CModelessDialog(UINT nIDTemplate, CWnd* pParent)
  {
    Create(nIDTemplate, pParent);
  }

protected:
  void PostNcDestroy() override
  {
    CDialog::PostNcDestroy();
    delete this;
  }
};

//     
template<class Derived, typename... Args>
Derived* CreateModelessDialog(Args&&... args)
{
  //  static_assert   ,   std::enable_if   ,     SFINAE. 
  //  ..       ,        .
  static_assert(std::is_base_of<CModelessDialog, Derived>::value, 
                "CreateModelessDialog should be called for descendants of CModelessDialog");
  auto* pDialog = new Derived(std::forward<Args>(args)...);
  pDialog->ShowWindow(SW_SHOW);
  return pDialog;
}

PostNcDestroy(), delete, , new. :

void CMainFrame::OnBnClickedCreate()
{
  CreateModelessDialog<CMyDialog>(this);
}

class CMyDialog : public CModelessDialog
{
public:
  CMyDialog(CWnd* pParent) : CModelessDialog(IDD_MY_DIALOG, pParent) {}
};

, . , . , . CModelessDialog. , , CMyDialog , , . .

, . new delete.

-

, GUI. Qt — UI.

QObject. , . ( ) .

, new delete . , . , (. Qt mailing list).

, new delete Qt.

std::locale::facet

++ std::locale. (facet), . , .

, , , new (. Notes std::locale):

std::locale default;
std::locale myLocale(default, new std::codecvt_utf8<wchar_t>);

.

, , new . , , .

, , . new delete make- .

, , new delete . , .

, , . , , new delete, , . , , .

:

• new delete . .
• .
• make- , .
• .

- new delete. , , , .

, , , .

C++ Russia. : , , , . , , , , , , .

PS , , : «» «». , «», . , «». , : «». -. , «», .

1. Herb Sutter, GotW #89 Solution: Smart Pointers.
2. Scott Meyers, Effective Modern C++, Item 21, p. 139.
3. Stephan T. Lavavej, Don’t Help the Compiler.
4. Bjarne Stroustrup, The C++ Programming Language, 11.2.1, p. 281.
5. Five Popular Myths about C++., Part 2
6. Mikhail Matrosov, C++ without new and delete.