ptr::ptr

Статья
10/16/2008

Constructs a com::ptr to wrap a COM object.

ptr();
ptr(
   _interface_type * p
);

Параметры

P
A COM interface pointer.

Заметки

The no-argument constructor assigns nullptr to the underlying object handle. Subsequent calls to the com::ptr will validate the internal object and silently fail until an object is actually created or attached.

The one-argument constructor adds a reference to the COM object but does not release the caller's reference, so the caller must call Release on the COM object to truly give up control. When the com::ptr's destructor is called it will automatically release its references on the COM object.

Passing NULL to this constructor is the same as calling the no-argument version.

Пример

This example implements a CLR class that uses a com::ptr to wrap its private member IXMLDOMDocument object. It demonstrates usage of both versions of the constructor.

// comptr_ptr.cpp
// compile with: /clr /link msxml2.lib
#include <msxml2.h>
#include <msclr\com\ptr.h>

#import <msxml3.dll> raw_interfaces_only

using namespace System;
using namespace System::Runtime::InteropServices;
using namespace msclr;

// a ref class that uses a com::ptr to contain an 
// IXMLDOMDocument object
ref class XmlDocument {
public:
   // construct the internal com::ptr with a null interface
   // and use CreateInstance to fill it
   XmlDocument(String^ progid) {
      m_ptrDoc.CreateInstance(progid);   
   }

   // construct the internal com::ptr with a COM object
   XmlDocument(IXMLDOMDocument* pDoc) : m_ptrDoc(pDoc) {}

   // note that the destructor will call the com::ptr destructor
   // and automatically release the reference to the COM object

private:
   com::ptr<IXMLDOMDocument> m_ptrDoc;
};

// use the ref class to handle an XML DOM Document object
int main() {
   IXMLDOMDocument* pDoc = NULL;

   try {
      // create an XML DOM document object
      Marshal::ThrowExceptionForHR(CoCreateInstance(CLSID_DOMDocument30, NULL, 
         CLSCTX_ALL, IID_IXMLDOMDocument, (void**)&pDoc));
      // construct the ref class with the COM object
      XmlDocument doc1(pDoc);

      // or create the class from a progid string
      XmlDocument doc2("Msxml2.DOMDocument.3.0");
   }
   // doc1 and doc2 destructors are called when they go out of scope
   // and the internal com::ptr releases its reference to the COM object
   catch (Exception^ e) {
      Console::WriteLine(e);   
   }
   finally {
      if (NULL != pDoc) {
         pDoc->Release();      
      }
   }
}