CComPtr Class

 

The latest version of this topic can be found at CComPtr Class.

A smart pointer class for managing COM interface pointers.

Syntax

template<class T>  
class CComPtr

Parameters

T
A COM interface specifying the type of pointer to be stored.

Members

Public Constructors

Name	Description
CComPtr::CComPtr	The constructor.

Public Operators

Name	Description
CComPtr::operator =	Assigns a pointer to the member pointer.

Remarks

ATL uses CComPtr and CComQIPtr to manage COM interface pointers. Both are derived from CComPtrBase, and both perform automatic reference counting.

The CComPtr and CComQIPtr classes can help eliminate memory leaks by performing automatic reference counting. The following functions both perform the same logical operations; however, note how the second version may be less error-prone by using the CComPtr class:

// Error-checking routine that performs manual lifetime management
// of a COM IErrorInfo object
HRESULT CheckComError_Manual()
{
   HRESULT hr;
   CComBSTR bstrDescription; 
   CComBSTR bstrSource; 
   CComBSTR bstrHelpFile; 

   IErrorInfo* pErrInfo = NULL; // naked COM interface pointer
   hr = ::GetErrorInfo(0, &pErrInfo);
   if(hr != S_OK)
      return hr;

   hr = pErrInfo->GetDescription(&bstrDescription); 
   if(FAILED(hr))
   {
      pErrInfo->Release();   // must release interface pointer before returning
      return hr;
   }

   hr = pErrInfo->GetSource(&bstrSource);
   if(FAILED(hr))
   {
      pErrInfo->Release();   // must release interface pointer before returning
      return hr;
   }

   hr = pErrInfo->GetHelpFile(&bstrHelpFile);
   if(FAILED(hr))
   {
      pErrInfo->Release();   // must release interface pointer before returning
      return hr;
   }

   pErrInfo->Release();      // must release interface pointer before returning
   return S_OK;
}

// Error-checking routine that performs automatic lifetime management
// of a COM IErrorInfo object through a CComPtr smart pointer object
HRESULT CheckComError_SmartPtr()
{
   HRESULT hr;
   CComBSTR bstrDescription; 
   CComBSTR bstrSource; 
   CComBSTR bstrHelpFile; 

   CComPtr<IErrorInfo> pErrInfo; 
   hr = ::GetErrorInfo(0, &pErrInfo);
   if(hr != S_OK)
      return hr;

   hr = pErrInfo->GetDescription(&bstrDescription); 
   if(FAILED(hr))
      return hr;

   hr = pErrInfo->GetSource(&bstrSource);
   if(FAILED(hr))
      return hr;

   hr = pErrInfo->GetHelpFile(&bstrHelpFile);
   if(FAILED(hr))
      return hr;

   return S_OK;
}   // CComPtr will auto-release underlying IErrorInfo interface pointer as needed

In Debug builds, link atlsd.lib for code tracing.

Inheritance Hierarchy

CComPtrBase

CComPtr

Requirements

Header: atlbase.h

CComPtr::CComPtr

The constructor.

CComPtr() throw ();
CComPtr(T* lp) throw ();
CComPtr (const CComPtr<T>& lp) throw ();

Parameters

lp
Used to initialize the interface pointer.

T
A COM interface.

CComPtr::operator =

Assignment operator.

T* operator= (T* lp) throw ();
T* operator= (const CComPtr<T>& lp) throw ();

Return Value

Returns a pointer to the updated CComPtr object

Remarks

This operation AddRefs the new object and releases the existing object, if one exists.

See Also

CComPtr::CComPtr
CComQIPtr::CComQIPtr
Class Overview