How to: Map HRESULTs and Exceptions 

COM methods report errors by returning HRESULTs; .NET methods report them by throwing exceptions. The runtime handles the transition between the two. Each exception class in the .NET Framework maps to an HRESULT.

User-defined exception classes can specify whatever HRESULT is appropriate. These exception classes can dynamically change the HRESULT to be returned when the exception is generated by setting the HResult field on the exception object. Additional information about the exception is provided to the client through the IErrorInfo interface, which is implemented on the .NET object in the unmanaged process.

If you create a class that extends System.Exception, you must set the HRESULT field during construction. Otherwise, the base class assigns the HRESULT value. You can map new exception classes to an existing HRESULT by supplying the value in the exception's constructor.

Note that the runtime will sometimes ignore an HRESULT in cases where there is an IErrorInfo present on the thread. This behavior can occur in cases where the HRESULT and the IErrorInfo do not represent the same error.

To create a new exception class and map it to an HRESULT

• Use the following code to create a new exception class called NoAccessException and map it to the HRESULT E_ACCESSDENIED.

  Class NoAccessException : public ApplicationException
  {
      NoAccessException () {
      HResult = E_ACCESSDENIED; 
  }
  }
  CMyClass::MethodThatThrows
  {
  throw new NoAccessException();
  }
  

You might encounter a program (in any programming language) that uses both managed and unmanaged code at the same time. For example, the custom marshaler in the following code example uses the Marshal.ThrowExceptionForHR(int HResult) method to throw an exception with a specific HRESULT value. The method looks up the HRESULT and generates the appropriate exception type. For example, the HRESULT in the following code fragment generates ArgumentException.

CMyClass::MethodThatThrows
{
    Marshal.ThrowExceptionForHR(COR_E_ARGUMENT);
}

The following table provides the complete mapping from each HRESULT to its comparable exception class in the .NET Framework.

HRESULT	.NET exception
MSEE_E_APPDOMAINUNLOADED	AppDomainUnloadedException
COR_E_APPLICATION	ApplicationException
COR_E_ARGUMENT or E_INVALIDARG	ArgumentException
COR_E_ARGUMENTOUTOFRANGE	ArgumentOutOfRangeException
COR_E_ARITHMETIC or ERROR_ARITHMETIC_OVERFLOW	ArithmeticException
COR_E_ARRAYTYPEMISMATCH	ArrayTypeMismatchException
COR_E_BADIMAGEFORMAT or ERROR_BAD_FORMAT	BadImageFormatException
COR_E_COMEMULATE_ERROR	COMEmulateException
COR_E_CONTEXTMARSHAL	ContextMarshalException
COR_E_CORE	CoreException
NTE_FAIL	CryptographicException
COR_E_DIRECTORYNOTFOUND or ERROR_PATH_NOT_FOUND	DirectoryNotFoundException
COR_E_DIVIDEBYZERO	DivideByZeroException
COR_E_DUPLICATEWAITOBJECT	DuplicateWaitObjectException
COR_E_ENDOFSTREAM	EndOfStreamException
COR_E_TYPELOAD	EntryPointNotFoundException
COR_E_EXCEPTION	Exception
COR_E_EXECUTIONENGINE	ExecutionEngineException
COR_E_FIELDACCESS	FieldAccessException
COR_E_FILENOTFOUND or ERROR_FILE_NOT_FOUND	FileNotFoundException
COR_E_FORMAT	FormatException
COR_E_INDEXOUTOFRANGE	IndexOutOfRangeException
COR_E_INVALIDCAST or E_NOINTERFACE	InvalidCastException
COR_E_INVALIDCOMOBJECT	InvalidComObjectException
COR_E_INVALIDFILTERCRITERIA	InvalidFilterCriteriaException
COR_E_INVALIDOLEVARIANTTYPE	InvalidOleVariantTypeException
COR_E_INVALIDOPERATION	InvalidOperationException
COR_E_IO	IOException
COR_E_MEMBERACCESS	AccessException
COR_E_METHODACCESS	MethodAccessException
COR_E_MISSINGFIELD	MissingFieldException
COR_E_MISSINGMANIFESTRESOURCE	MissingManifestResourceException
COR_E_MISSINGMEMBER	MissingMemberException
COR_E_MISSINGMETHOD	MissingMethodException
COR_E_MULTICASTNOTSUPPORTED	MulticastNotSupportedException
COR_E_NOTFINITENUMBER	NotFiniteNumberException
E_NOTIMPL	NotImplementedException
COR_E_NOTSUPPORTED	NotSupportedException
COR_E_NULLREFERENCE orE_POINTER	NullReferenceException
COR_E_OUTOFMEMORY or E_OUTOFMEMORY	OutOfMemoryException
COR_E_OVERFLOW	OverflowException
COR_E_PATHTOOLONG or ERROR_FILENAME_EXCED_RANGE	PathTooLongException
COR_E_RANK	RankException
COR_E_REFLECTIONTYPELOAD	ReflectionTypeLoadException
COR_E_REMOTING	RemotingException
COR_E_SAFEARRAYTYPEMISMATCH	SafeArrayTypeMismatchException
COR_E_SECURITY	SecurityException
COR_E_SERIALIZATION	SerializationException
COR_E_STACKOVERFLOW orERROR_STACK_OVERFLOW	StackOverflowException
COR_E_SYNCHRONIZATIONLOCK	SynchronizationLockException
COR_E_SYSTEM	SystemException
COR_E_TARGET	TargetException
COR_E_TARGETINVOCATION	TargetInvocationException
COR_E_TARGETPARAMCOUNT	TargetParameterCountException
COR_E_THREADABORTED	ThreadAbortException
COR_E_THREADINTERRUPTED	ThreadInterruptedException
COR_E_THREADSTATE	ThreadStateException
COR_E_THREADSTOP	ThreadStopException
COR_E_TYPELOAD	TypeLoadException
COR_E_TYPEINITIALIZATION	TypeInitializationException
COR_E_VERIFICATION	VerificationException
COR_E_WEAKREFERENCE	WeakReferenceException
COR_E_VTABLECALLSNOTSUPPORTED	VTableCallsNotSupportedException
All other HRESULTs	COMException

To retrieve extended error information, the managed client must examine the fields of the exception object that was generated. For the exception object to provide useful information about an error, the COM object must implement the IErrorInfo interface. The runtime uses the information provided by IErrorInfo to initialize the exception object.

If the COM object does not support IErrorInfo, the runtime initializes an exception object with default values. The following table lists each field associated with an exception object and identifies the source of default information when the COM object supports IErrorInfo.

Note that the runtime will sometimes ignore an HRESULT in cases where there is an IErrorInfo present on the thread. This behavior can occur in cases where the HRESULT and the IErrorInfo do not represent the same error.

---

Exception field	Source of Information from COM
ErrorCode	HRESULT returned from call.
HelpLink	If IErrorInfo->HelpContext is nonzero, the string is formed by concatenating IErrorInfo->GetHelpFile and "#" and IErrorInfo->GetHelpContext. Otherwise the string is returned from IErrorInfo->GetHelpFile.
InnerException	Always a null reference (Nothing in Visual Basic).
Message	String returned from IErrorInfo->GetDescription.
Source	String returned from IErrorInfo->GetSource.
StackTrace	The stack trace.
TargetSite	The name of the method that returned the failing HRESULT.

Exception fields, such as Message, Source, and StackTrace are not available for the StackOverflowException.

See Also

Other Resources

Advanced COM Interoperability
Handling and Throwing Exceptions