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新規および削除なしのC ++

, !

, Align Technology. ++.

, . , ++ . , — .

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

, , . , . , .

, , - .


behappy.me

: new delete . , . , .

:

, 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 , . 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- , :

. , 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. , , , .

, , , .

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.


Source: https://habr.com/ru/post/J283352/

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