关于FileSeek的问题

Question

iFileLength老是返回-1,请问各位前辈这是什么原因呢?谢谢!
procedure TForm1.MenuItem1Click(Sender: TObject);
var
   iFileHandle:THandle;
   iFileLength:LongInt;
   iByteRead:LongInt;
   Buffer:PChar;
   i:LongInt;
const
   FOffset=1;//偏移量
   Origin=0; //起始位置
begin
     if OpenDialog1.Execute then begin
        //self.Caption:=OpenDialog1.FileName;
        try
           iFileHandle:=FileOpen(OpenDialog1.FileName,fmOpenReadWrite);
           if iFileHandle=0 then begin
               ShowMessage('打开Txt文件失败');
               Abort;
           end;
           iFileLength:=FileSeek(iFileHandle,FOffset,Origin);//iFileLength老是返回-1,请问各位前辈这是什么原因呢?谢谢!           ShowMessage(IntToStr(iFileLength));
        finally        end;
     end;
end;     

Answer 1

iFileLength   :=   FileSeek(fh,0,2);//文件总长度