Fill the CXlOper with a formatted string (like sprintf() and CString::Format())
[C++]
BOOL Format(
   const char* lpszFormat,
    ...
);
BOOL Format(
   UINT idFormat,
    ...
);
A formatting string, exactly like those used by sprintf.
The values to be substituted into the output string in place of the tokens in the template string.
The resource ID of a formatting string, exactly like those used by sprintf.
The result of the SDK call-back. xlretSuccess (0) indicates success. 
            Other values indicate failure. 
            A full list of return values can be found in the section "Return codes" in 
            the MS SDK header file XLCALL32.H.
This function places a string into the CXlOper which calls it. 
            The string is formatted using the template string in exactly the same way as sprintf().
            For example:
CXlOper xloResult;
xloResult.Format("#ERROR: Result code %d", rc);
Header: xllplus.h