The signed keyword indicates the most significant bit of an integer variable represents a sign bit rather than a data bit.
[[ signed ]] type-qualifier [[ int ]]identifier-name;
Specifies a valid MIDL identifier. Valid MIDL identifiers consist of up to 31 alphanumeric and/or underscore characters and must start with an alphabetic or underscore character.
This keyword is optional and can be used with any of the character and integer types char, wchar_t, long, short, and small. You can optionally include the keyword int after the type qualifiers 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, specify the sign of the integer and character types.