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How to: Map HRESULTs and Exceptions

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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

  1. 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 marshaller 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 common mappings from HRESULT to its comparable exception class in .NET. HRESULT values without explicit mappings are mapped to COMException. The complete up-to-date mapping can be found in the dotnet/runtime repository.

HRESULT .NET exception
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_DIRECTORYNOTFOUND or ERROR_PATH_NOT_FOUND DirectoryNotFoundException
COR_E_DIVIDEBYZERO DivideByZeroException
COR_E_DUPLICATEWAITOBJECT DuplicateWaitObjectException
COR_E_ENDOFSTREAM EndOfStreamException
COR_E_ENTRYPOINTNOTFOUND 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_INVALIDFILTERCRITERIA InvalidFilterCriteriaException
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_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_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_THREADINTERRUPTED ThreadInterruptedException
COR_E_THREADSTATE ThreadStateException
COR_E_TYPELOAD TypeLoadException
COR_E_TYPEINITIALIZATION TypeInitializationException
COR_E_VERIFICATION VerificationException

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