The signed keyword indicates that the most significant bit of an integer variable represents a sign bit rather than a data bit. This keyword is optional and can be used with any of the character and integer types char, wchar_t, long, short, and small.
When you use the MIDL compiler switch char, character and integer types that appear in the IDL file without explicit sign keywords can appear with the signed or unsigned keywords in the generated header file. To avoid confusion, explicitly specify the sign of the integer and character types.
base_types, IDL, int, long, short, small, unsigned