CAutoPtr Class

 

For the latest documentation on Visual Studio 2017 RC, see Visual Studio 2017 RC Documentation.

This class represents a smart pointer object.

System_CAPS_ICON_important.jpg Important

This class and its members cannot be used in applications that execute in the Windows Runtime.

template <typename T>  
class CAutoPtr

Parameters

T
The pointer type.

Public Constructors

NameDescription
CAutoPtr::CAutoPtrThe constructor.
CAutoPtr::~CAutoPtrThe destructor.

Public Methods

NameDescription
CAutoPtr::AttachCall this method to take ownership of an existing pointer.
CAutoPtr::DetachCall this method to release ownership of a pointer.
CAutoPtr::FreeCall this method to delete an object pointed to by a CAutoPtr.

Public Operators

NameDescription
CAutoPtr::operator T*The cast operator.
CAutoPtr::operator =The assignment operator.
CAutoPtr::operator ->The pointer-to-member operator.

Public Data Members

NameDescription
CAutoPtr::m_pThe pointer data member variable.

This class provides methods for creating and managing a smart pointer, which will help protect against memory leaks by automatically freeing resources when it falls out of scope.

Further, CAutoPtr's copy constructor and assignment operator transfer ownership of the pointer, copying the source pointer to the destination pointer and setting the source pointer to NULL. It is therefore impossible to have two CAutoPtr objects each storing the same pointer, and this reduces the possibility of deleting the same pointer twice.

CAutoPtr also simplifies the creation of collections of pointers. Instead of deriving a collection class and overriding the destructor, it's simpler to make a collection of CAutoPtr objects. When the collection is deleted, the CAutoPtr objects will go out of scope and automatically delete themselves.

CHeapPtr and variants work in the same way as CAutoPtr, except that they allocate and free memory using different heap functions instead of the C++ new and delete operators. CAutoVectorPtr is similar to CAutoPtr, the only difference being that it uses vector new[] and vector delete[] to allocate and free memory.

See also CAutoPtrArray and CAutoPtrList when arrays or lists of smart pointers are required.

Header: atlbase.h

// A simple class for demonstration purposes

class MyClass 
{
   int iA;
   int iB;
public:
   MyClass(int a, int b);
   void Test();
};

MyClass::MyClass(int a, int b)
{
   iA = a;
   iB = b;
}

void MyClass::Test()
{
   ATLASSERT(iA == iB);
}

// A simple function

void MyFunction(MyClass* c)
{
   c->Test();
}

int UseMyClass()
{
   // Create an object of MyClass.
   MyClass *pMyC = new MyClass(1, 1);

   // Create a CAutoPtr object and have it take
   // over the pMyC pointer by calling Attach.
   CAutoPtr<MyClass> apMyC;
   apMyC.Attach(pMyC);

   // The overloaded -> operator allows the 
   // CAutoPtr object to be used in place of the pointer.
   apMyC->Test();

   // Assign a second CAutoPtr, using the = operator.
   CAutoPtr<MyClass> apMyC2;
   apMyC2 = apMyC;

   // The casting operator allows the
   // object to be used in place of the pointer.
   MyFunction(pMyC);
   MyFunction(apMyC2);

   // Detach breaks the association, so after this
   // call, pMyC is controlled only by apMyC.
   apMyC2.Detach();

   // CAutoPtr destroys any object it controls when it
   // goes out of scope, so apMyC destroys the object 
   // pointed to by pMyC here.
   return 0;
}

Call this method to take ownership of an existing pointer.

void Attach(T* p) throw();

Parameters

p
The CAutoPtr object will take ownership of this pointer.

Remarks

When a CAutoPtr object takes ownership of a pointer, it will automatically delete the pointer and any allocated data when it goes out of scope. If CAutoPtr::Detach is called, the programmer is again given responsibility for freeing any allocated resources.

In debug builds, an assertion failure will occur if the CAutoPtr::m_p data member currently points to an existing value; that is, it is not equal to NULL.

Example

See the example in the CAutoPtr Overview.

The constructor.

CAutoPtr() throw();
explicit CAutoPtr(T* p) throw();

template<typename TSrc>
CAutoPtr(CAutoPtr<TSrc>& p) throw();

template<> 
CAutoPtr(CAutoPtr<T>& p) throw();

Parameters

p
An existing pointer.

TSrc
The type being managed by another CAutoPtr, used to initialize the current object.

Remarks

The CAutoPtr object can be created using an existing pointer, in which case it transfers ownership of the pointer.

Example

See the example in the CAutoPtr Overview.

The destructor.

~CAutoPtr() throw();

Remarks

Frees any allocated resources. Calls CAutoPtr::Free.

Call this method to release ownership of a pointer.

T* Detach() throw();

Return Value

Returns a copy of the pointer.

Remarks

Releases ownership of a pointer, sets the CAutoPtr::m_p data member variable to NULL, and returns a copy of the pointer. After calling Detach, it is up to the programmer to free any allocated resources over which the CAutoPtr object may have previously assumed reponsibility.

Example

See the example in the CAutoPtr Overview.

Call this method to delete an object pointed to by a CAutoPtr.

void Free() throw();

Remarks

The object pointed to by the CAutoPtr is freed, and the CAutoPtr::m_p data member variable is set to NULL.

The pointer data member variable.

T* m_p;

Remarks

This member variable holds the pointer information.

The assignment operator.

template<>
CAutoPtr<T>& operator= (CAutoPtr<T>& p);

template<typename TSrc>
CAutoPtr<T>& operator= (CAutoPtr<TSrc>& p);

Parameters

p
A pointer.

TSrc
A class type.

Return Value

Returns a reference to a CAutoPtr< T >.

Remarks

The assignment operator detaches the CAutoPtr object from any current pointer and attaches the new pointer, p, in its place.

Example

See the example in the CAutoPtr Overview.

The pointer-to-member operator.

T* operator->() const throw();

Return Value

Returns the value of the CAutoPtr::m_p data member variable.

Remarks

Use this operator to call a method in a class pointed to by the CAutoPtr object. In debug builds, an assertion failure will occur if the CAutoPtr points to NULL.

Example

See the example in the CAutoPtr Overview.

The cast operator.

operator T*() const throw();

Return Value

Returns a pointer to the object data type defined in the class template.

Example

See the example in the CAutoPtr Overview.

CHeapPtr Class
CAutoVectorPtr Class
Class Overview

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