函数如何返回array of byte(20分)

小弟先拜大虾了，如何将字符串转变为比特数组？[]

procedure TForm1.Button1Click(Sender: TObject);
type TByteArray=Array of Byte;
function GetStr:TByteArray;
begin
SetLength(Result,100);
StrPCopy(PChar(@Result[0]),'aaaaaaaaaaa');
end;
var B:TByteArray;
begin
B:=GetStr;
ShowMessage(Pchar(@B[0]));
end;

Str:String;
i:Integer;
b:array[0..3]of byte

Str:='1fgs';
for i:=1 to 4 do
b[i-1]:=byte(Str);