Delphi Tips

Find all Local Computers on a LAN

How to use WinAPI to find the
computers on the LAN? Call
FindComputers, which returns the
WinAPI error code (if any).

The function will fill the
stringlist Computers with the
computer names. It is developed with Delphi 5, but
should be backward-compatible.

unit FindComp;

interface

uses
  Windows, Classes;

function FindComputers: DWORD;

var
  Computers: TStringList;

implementation

uses
  SysUtils;

const
  MaxEntries = 250;

function FindComputers: DWORD;

var
  EnumWorkGroupHandle, 
  EnumComputerHandle  : THandle;
  EnumError           : DWORD;
  Network             : TNetResource;
  WorkGroupEntries, 
  ComputerEntries     : DWORD;
  EnumWorkGroupBuffer,
  EnumComputerBuffer : array[1..MaxEntries] of 
                                          TNetResource;
  EnumBufferLength    : DWORD;
  I, J                : DWORD;

begin

  Computers.Clear;

  FillChar(Network, SizeOf(Network), 0);
  with Network do
  begin
    dwScope := RESOURCE_GLOBALNET;
    dwType := RESOURCETYPE_ANY;
    dwUsage := RESOURCEUSAGE_CONTAINER;
  end;

  EnumError := WNetOpenEnum(RESOURCE_GLOBALNET, 
                            RESOURCETYPE_ANY, 0, 
                            @Network, 
                            EnumWorkGroupHandle);

  if EnumError = NO_ERROR then
  begin
    WorkGroupEntries := MaxEntries;
    EnumBufferLength := SizeOf(EnumWorkGroupBuffer);
    EnumError := WNetEnumResource(EnumWorkGroupHandle, 
                                 WorkGroupEntries, 
                                 @EnumWorkGroupBuffer, 
                                 EnumBufferLength);

    if EnumError = NO_ERROR then
    begin
      for I := 1 to WorkGroupEntries do
      begin
        EnumError := WNetOpenEnum(RESOURCE_GLOBALNET,
                                RESOURCETYPE_ANY, 0,
                                @EnumWorkGroupBuffer[I],
                                EnumComputerHandle);
        if EnumError = NO_ERROR then
        begin
          ComputerEntries := MaxEntries;
          EnumBufferLength:= SizeOf(EnumComputerBuffer);
        EnumError:=WNetEnumResource(EnumComputerHandle,
                                    ComputerEntries,
                                    @EnumComputerBuffer,
                                    EnumBufferLength);
          if EnumError = NO_ERROR then
            for J := 1 to ComputerEntries do
              Computers.Add(Copy(EnumComputerBuffer[J].
               lpRemoteName, 3, 
              Length(EnumComputerBuffer[J].
               lpRemoteName) - 2));
          WNetCloseEnum(EnumComputerHandle);
        end;
      end;
    end;
    WNetCloseEnum(EnumWorkGroupHandle);
  end;

  if EnumError = ERROR_NO_MORE_ITEMS then
    EnumError := NO_ERROR;
  Result := EnumError;

end;

initialization

  Computers := TStringList.Create;

finalization

  Computers.Free;

end.

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