关于在COM中使用可选参数的研究[1]

function varisemptyparam(const v: variant): boolean;

begin

  result := (tvardata(v).vtype = varerror) and

            (tvardata(v).verror = $80020004); {disp_e_paramnotfound}

end;

uses comserv, variants, dialogs, sysutils;

procedure toptionalparamsdemo.getparams(const param1: widestring; param2,param3: olevariant; param4: integer);

var

  s2, s3: widestring;

begin

  if varisemptyparam(param2) then

    s2 := ' empty '

  else

    s2 := ' not empty ';

  if varisemptyparam(param3) then

    s3 := ' empty '

  else

    s3 := ' not empty ';

  showmessage(format('param1[%s] param2[%s] param3[%s] param4[%d]',[param1, s2, s3, param4]));

end;