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Introducing three different approaches to get local IP address in Delphi: Winsock, TIdStack and TIdIPWatch.

1) Get local IP address by Winsock

uses Winsock;

.
.
.

function GetLocalIP: string;
type
  TaPInAddr = array [0..10] of PInAddr;
  PaPInAddr = ^TaPInAddr;
var
  phe: PHostEnt;
  pptr: PaPInAddr;
  Buffer: array [0..63] of Ansichar;
  i: Integer;
  GInitData: TWSADATA;
begin
  WSAStartup($101, GInitData);
  Result := '';
  GetHostName(Buffer, SizeOf(Buffer));
  phe := GetHostByName(Buffer);
  if phe = nil then
    Exit;
  pptr := PaPInAddr(phe^.h_addr_list);
  i := 0;
  while pptr^[i] <> nil do
  begin
    Result := StrPas(inet_ntoa(pptr^[i]^));
    Inc(i);
  end;
  WSACleanup;
end;


2) Get local IP address by TIDStack Indy class

uses IdStack;

.
.
.

function GetIP : String;
begin
  TIdStack.IncUsage;
  try
    Result := GStack.LocalAddress;
  finally
    TIdStack.DecUsage;
  end;
end


3) Get local IP address by TIdIpWatch Indy component

uses IdBaseComponent, IdComponent, IdIPWatch;

.
.
.

function GetLocalIp: string;
var 
   IPW: TIdIPWatch;
begin   
  IpW := TIdIPWatch.Create(nil);
  try
    if IpW.LocalIP <> '' then
      Result := IpW.LocalIP;
  finally
    IpW.Free;
  end;
end;