Using New Data Types in Your IDL File
The Basetsd.h header file defines the new data types needed for writing applications that run on both 32- and 64-bit Windows. To use these data types in your interfaces, import Basetsd.h into your IDL file. Do not #include the file or you will end up with multiple definitions at compile time.
Alternatively, you can include or import the Basetsd.idl file into your IDL file.
For more information on adding system header files to your IDL file, see Importing Files and Type Libraries and Importing System Header Files.