Optional

Optional indicates that an actual parameter may not be specified for this formal parameter. The external function is called with a zero value of the specified type, which is false for Boolean, 0 for integer numbers, 0.0 for floating point numbers, NULL for string types, and an empty list of unspecified type, which must not be modified, for lists.

注: All formal parameters on the right of an optional must also be optional.

Example

dll "some.dll"
  "DoOptional"
    function DoOptional (nParam1 : out number optional,
                         nParam2 : in number optional);

dcltrans
  transaction TMain
  begin
    // both actual parameters can be omitted
    DoOptional();
  end TMain;