Determine your local IP using Winsock

Problem/Question/Abstract:

Determine your local IP using Winsock

Answer:

The code below uses the WinSock unit to lookup your local IP number. Simply call the function LocalIP - it will return your IP as a string.

In a LAN, it will return your local IP number, e.g. 192.168.100.25, not your external IP number.


unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, WinSock;

type
  TForm1 = class(TForm)
    Label1: TLabel;
    Button1: TButton;
    Memo1: TMemo;
    procedure FormCreate(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

function LocalIP: string;
type
  TArrayPInAddr = array[0..10] of PInAddr;
  PArrayPInAddr = ^TArrayPInAddr;
var
  phe: PHostEnt;
  pptr: PArrayPInAddr;
  Buffer: array[0..63] of char;
  i: integer;
  GInitData: TWSADATA;
begin
  WSAStartup($101, GInitData);
  result := '';
  GetHostName(Buffer, sizeof(Buffer));
  phe := GetHostByName(Buffer);
  if phe = nil then
  begin
    exit
  end;
  pptr := PArrayPInAddr(phe^.h_addr_list);
  i := 0;
  while pptr^[i] <> nil do
  begin
    result := StrPas(inet_ntoa(pptr^[i]^));
    Inc(i);
  end;
  WSACleanup;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  ShowMessage('Your computer''s IP address is: ' + LocalIP);
end;

end.