function IPAddrToName(IPAddr: string): string; 
//函数返回值就是机器名
var
  SockAddrIn: TSockAddrIn;
  HostEnt: PHostEnt;
  WSAData: TWSAData;
begin
  WSAStartup($101, WSAData);
  SockAddrIn.sin_addr.s_addr := inet_addr(PChar(IPAddr));
  HostEnt := gethostbyaddr(@SockAddrIn.sin_addr.S_addr, 4, AF_INET);
  if HostEnt <> nil then
    Result := StrPas(Hostent^.h_name)
  else
    Result := '';
end;
//测试
procedure TForm1.Button2Click(Sender: TObject);
begin
  Edit2.Text:=IPAddrToName('192.168.0.1');
end;