DELPHI 检测URL地址是否有效

function TForm1.CheckUrl(url: string):Boolean;
var
hSession, hfile, hRequest: HINTERNET;
dwindex, dwcodelen: dword;
dwcode: array[1..20] of Char; res: PChar;
begin
Result := false;
if Pos('http://',LowerCase(url)) = 0 then url := 'http://' + url;
{ Open an internet session }
hSession:=InternetOpen('InetURL:/1.0',INTERNET_OPEN_TYPE_PRECONFIG,nil,nil, 0);
if Assigned(hsession) then
begin
hfile := InternetOpenUrl(hsession, PChar(url), nil, 0,INTERNET_FLAG_RELOAD, 0);
dwIndex := 0;
dwCodeLen := 10;
HttpQueryInfo(hfile,HTTP_QUERY_STATUS_CODE,@dwcode,dwcodeLen,dwIndex);
res := PChar(@dwcode);
Result := (res = '200') or (res = '302');
if Assigned(hfile) then
InternetCloseHandle(hfile);
InternetCloseHandle(hsession);
end;
end;