ptr::operator bool

Artigo
12/18/2017

The latest version of this topic can be found at ptr::operator bool.

Operator for using com::ptr in a conditional expression.

Syntax

operator bool();

Return Value

true if the owned COM object is valid; false otherwise.

Remarks

The owned COM object is valid if it is not nullptr.

This operator actually converts to _detail_class::_safe_bool which is safer than bool because it cannot be converted to an integral type.

Example

This example implements a CLR class that uses a com::ptr to wrap its private member IXMLDOMDocument object. The CreateInstance member function uses operator bool after creating the new document object to determine if it is valid and writes to the console if it is.

// comptr_op_bool.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:  
   void CreateInstance(String^ progid) {  
      if (!m_ptrDoc) {  
         m_ptrDoc.CreateInstance(progid);     
         if (m_ptrDoc) { // uses operator bool  
            Console::WriteLine("DOM Document created.");  
         }  
      }  
   }  
  
   // 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() {  
   try {  
      XmlDocument doc;  
      // create the instance from a progid string  
      doc.CreateInstance("Msxml2.DOMDocument.3.0");  
   }  
   catch (Exception^ e) {  
      Console::WriteLine(e);     
   }  
}

DOM Document created.

Requirements

Header file <msclr\com\ptr.h>

Namespace msclr::com

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