RoTransformErrorW function

Reports a transformed error and an informative string to an attached debugger.


BOOL WINAPI RoTransformErrorW(
  _In_ HRESULT oldError,
  _In_ HRESULT newError,
  _In_ UINT    cchMax,
  _In_ PCWSTR  message


oldError [in]


The original error code associated with the error condition.

newError [in]


The custom error code to associate with the error condition. If oldError and newError are the same, or both are success codes, such as S_OK, the function has no effect and returns FALSE.

cchMax [in]

Type: UINT

The maximum number of characters in message, excluding the terminating null character. If the value is 0, the string is read to the first null character or 512 characters, whichever is less. If cchMax is greater than 512, all characters after 512 are ignored.

message [in]


An informative string to help developers to correct the reported error condition. The maximum length is 512 characters, including the trailing null character; longer strings are truncated.

If the string is empty, the function succeeds but no error information is reported. It is recommended that you always provide an informative string.

If message is NULL, the function succeeds and reports the generic string in Winerror.h if available or the generic string associated with E_FAIL.

This function does not support embedded null characters, so only the characters before the first null are reported.

Return value

Type: BOOL

Return codeDescription

The error message was reported successfully.


message is NULL or points to an empty string, or oldError and newError are the same, or both are success codes.



Use the RoTransformErrorW function to substitute a custom error code for an existing error condition. For example, if the current error condition is E_FAIL, you can substitute a more specific error code, such as E_FILENOTFOUND and report the transformed error to an attached debugger.

The behavior of the RoTransformErrorW function is otherwise the same as the RoOriginateErrorW function.

If the UseSetErrorInfo flag is set by calling the RoSetErrorReportingFlags function, and the calling thread has been initialized in COM, the function creates an appropriate error object that supports IRestrictedErrorInfo and associates it with the COM channel by calling SetErrorInfo. If the thread has not been initialized into COM, the call will still succeed with no error, but the error will not be associated with the COM channel.

Note  This is no ANSI version of the RoTransformErrorW function. Message strings are required to be Unicode.


Minimum supported client

Windows 8 [desktop apps | Windows Store apps]

Minimum supported server

Windows Server 2012 [desktop apps | Windows Store apps]

Minimum supported phone

Windows Phone 8



See also