Hi,

I need a way to test if an string containing an ipv4-address is really
an ipv4-address.
I tried
tmpAddress:=HostAddrToStr(StrToHostAddr(IPAddressStr));
writeln(tmpAddress);
  if (tmpAddress='0.0.0.0') then
   begin
    writeln('Error in IP-address');
    IPAddressStr:=tmpAddress;
   end;
When I enter 192.168.185.297 (i.e. not a valid ipv4 address) in
IPAddressStr I get
192.168.185.41
not the expected error-message.

According to the rtl-manual :

function StrToHostAddr(IP: AnsiString) : in_addr
Description: StrToHostAddr converts the string representation in IP to a host address and returns the host
address.
Errors: On error, the host address is filled with zeroes.

I would think that converting those zeroes to a host-address would yield 0.0.0.0.

Am I missing something ?
Is there a better way, without using some other network-library ?

Koenraad.

You can add a multiple of 256 to any octet of an IPv4 address in most programs. Try it in your browser, it will probably also work.

Jonas

The IP-Adress is a dword, but you can change, that it fits for you.

function str_getval( str : shortstring ) : longint;
var cod : longint;
begin
 val( str , result , cod );
end;
function ip_from_string( ipstr : shortstring ; out error : boolean ) : dword;
var
 c : char;
 ipn , pointanz : longint;
 x : longint;
 pstr : shortstring;
 ip : dword;
 procedure add_ip;
 begin
  ipn := str_getval( pstr );
  if ( ipn > 255 ) or ( pstr = '' ) then error := true;
  ip := ip shl 8;
  ip := ip or ipn;
  pstr := '';
 end;
begin
 ip := 0;
 pstr := '';
 error := false;
 pointanz := 0;
 for x := 1 to length( ipstr ) do begin
  c := ipstr[ x ];
  case c of
   '0'..'9' : pstr := pstr + c;
   '.' : begin
    inc( pointanz );
    add_ip;
   end;
   else error := true;
  end;
 end;
 add_ip;
 if pointanz  3 then error := true;
 if error then result := 0
          else result := ip;
end;

What browser supports that?

Mattias

The in_addr IP address type is a packed record of byte, so if an IP address part larger than 255 is encountered in a string it will be truncated when copied to the byte record using StrToHostAddr. This probably means you have to use some other means of detecting an invalid address, or add a check for (tmpAddress IPAddressStr) to cater for your situation.

In Firefox 45.2.0 on Linux it does not work.
It is confusing anyway.

Op 28-07-16 om 10:38 schreef Christo:

Thanks,

I used the check :
(tmpAddress IPAddressStr)
in stead of
(tmpAddress='0.0.0.0')

Koenraad