var
  bs: array[0..25] of Byte;
  s: string;
  i: Integer;
begin
  for i := 0 to Length(bs) - 1 do bs[i] := 65+i;
  s := string(StrPas(PAnsiChar(@bs)));
  ShowMessage(s); {ABCDEFGHIJKLMNOPQRSTUVWXYZ}
end;

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{汉字到多字节编码}
procedure TForm1.Button1Click(Sender: TObject);
var
  stream: TStringStream;
  b: Byte;
  s: string;
begin
  stream := TStringStream.Create('我们', TEncoding.Default);
  s := '';
  for b in stream.Bytes do s := Format('%s%x ', [s,b]);

  ShowMessage(s); {CE D2 C3 C7}
  stream.Free;
end;

{多字节编码到汉字}
procedure TForm1.Button2Click(Sender: TObject);
var
  stream: TStringStream;
begin
  stream := TStringStream.Create;
  stream.Size := 4;
  stream.Bytes[0] := $CE; 
  stream.Bytes[1] := $D2;
  stream.Bytes[2] := $C3;
  stream.Bytes[3] := $C7;

  ShowMessage(stream.DataString); {我们}
  stream.Free;
end;

{把多字节编码的字符串转换到汉字}
procedure TForm1.Button3Click(Sender: TObject);
var
  str: AnsiString;
  stream: TStringStream;
  i: Integer;
begin
  str := 'CED2C3C7';
  stream := TStringStream.Create;
  stream.Size := Length(str) div 2;

  for i := 1 to Length(str) do
    if Odd(i) then
      stream.Bytes[i div 2] := StrToIntDef(Concat(#36,str[i],str[i+1]), 0);

  ShowMessage(stream.DataString); {我们}
  stream.Free;
end;

end.

{函数}
function SetScreen(x,y: Word): Boolean;
var
  DevMode: TDeviceMode;
begin
  Result := EnumDisplaySettings(nil, 0, DevMode);
  if Result then
  begin
    DevMode.dmFields := DM_PELSWIDTH or DM_PELSHEIGHT;
    DevMode.dmPelsWidth := x;
    DevMode.dmPelsHeight := y;
    Result := ChangeDisplaySettings(DevMode, 0) = DISP_CHANGE_SUCCESSFUL;
  end;
end;

{测试}
procedure TForm1.Button1Click(Sender: TObject);
begin
  SetScreen(1024, 768);
end;

var
  bs: TBytes;
  b: Byte;
  str: string;
begin
  {只有 Unicode、BigEndianUnicode、UTF8 编码有识别符}
  bs := TEncoding.Unicode.GetPreamble;
  str := '';
  for b in bs do str := Format('%s %x', [str, b]);
  ShowMessage(str); {FF FE}

  bs := TEncoding.BigEndianUnicode.GetPreamble;
  str := '';
  for b in bs do str := Format('%s %x', [str, b]);
  ShowMessage(str); {FE FF}

  bs := TEncoding.UTF8.GetPreamble;
  str := '';
  for b in bs do str := Format('%s %x', [str, b]);
  ShowMessage(str); {EF BB BF}

  {ASCII、UTF7 和 Default(默认编码) 没有识别符}
  bs := TEncoding.ASCII.GetPreamble;
  str := '';
  for b in bs do str := Format('%s %x', [str, b]);
  ShowMessage(str); {无}

  bs := TEncoding.UTF7.GetPreamble;
  str := '';
  for b in bs do str := Format('%s %x', [str, b]);
  ShowMessage(str); {无}

  bs := TEncoding.Default.GetPreamble;
  str := '';
  for b in bs do str := Format('%s %x', [str, b]);
  ShowMessage(str); {无} 
end;