[fpc-pascal] Test for valid ip address

[Rainer Stratmann]

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;



Am Donnerstag, 28. Juli 2016, 10:14:10 schrieb Koenraad Lelong:
> 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.
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