ptr::operator=
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The latest version of this topic can be found at ptr::operator=.
Attaches a COM object to a com::ptr
.
ptr<_interface_type> % operator=(
_interface_type * _right
);
_right
The COM interface pointer to attach.
A tracking reference on the com::ptr
.
If the com::ptr
already owns a reference to a COM object, operator=
throws InvalidOperationException.
Assigning a COM object to a com::ptr
references the COM object but does not release the caller's reference to it.
This operator has the same effect as Attach
.
This example implements a CLR class that uses a com::ptr
to wrap its private member IXMLDOMDocument
object. The ReplaceDocument
member function first calls Release
on any previously owned object and then uses operator=
to attach a new document object.
// comptr_op_assign.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);
}
// replace currently held COM object with another one
void ReplaceDocument(IXMLDOMDocument* pDoc) {
// release current document object
m_ptrDoc.Release();
// attach the new document object
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;
};
// unmanaged function that creates a raw XML DOM Document object
IXMLDOMDocument* CreateDocument() {
IXMLDOMDocument* pDoc = NULL;
Marshal::ThrowExceptionForHR(CoCreateInstance(CLSID_DOMDocument30, NULL,
CLSCTX_INPROC_SERVER, IID_IXMLDOMDocument, (void**)&pDoc));
return pDoc;
}
// use the ref class to handle an XML DOM Document object
int main() {
IXMLDOMDocument* pDoc = NULL;
try {
// create the class from a progid string
XmlDocument doc("Msxml2.DOMDocument.3.0");
// get another document object from unmanaged function and
// store it in place of the one held by the ref class
pDoc = CreateDocument();
doc.ReplaceDocument(pDoc);
// no further need for raw object reference
pDoc->Release();
pDoc = NULL;
}
catch (Exception^ e) {
Console::WriteLine(e);
}
finally {
if (NULL != pDoc) {
pDoc->Release();
}
}
}
Header file <msclr\com\ptr.h>
Namespace msclr::com