编码转换 unicode gbk big5

function UnicodeEncode(Str:string;CodePage:integer):WideString;
var
  Len:integer;
begin
  Len:=Length(Str)+1;
  SetLength(Result,Len);
  Len:=MultiByteToWideChar(CodePage,0,PChar(Str),-1,PWideChar(Result),Len);
  SetLength(Result,Len-1); //end is #0
end;

function UnicodeDecode(Str:WideString;CodePage:integer):string;
var
  Len:integer;
begin
  Len:=Length(Str)*2+1;  //one for #0
  SetLength(Result,Len);
  Len:=WideCharToMultiByte(CodePage,0,PWideChar(Str),-1,PChar(Result),Len,nil,nil);
  SetLength(Result,Len-1);
end;

function Gb2Big5(Str:string):string;
begin
  SetLength(Result,Length(Str));
  LCMapString(GetUserDefaultLCID,LCMAP_TRADITIONAL_CHINESE,
    PChar(Str),Length(Str),
    PChar(Result),Length(Result));
  Result:=UnicodeDecode(UnicodeEncode(Result,936),950);
end;

function Big52Gb(Str:string):string;
begin
  Str:=UnicodeDecode(UnicodeEncode(Str,950),936);
  SetLength(Result,Length(Str));
  LCMapString(GetUserDefaultLCID,LCMAP_SIMPLIFIED_CHINESE,
    PChar(Str),Length(Str),
    PChar(Result),Length(Result));
end;

关键使用了UnicodeToUtf8这个函数
function Utf8Encode(const WS: WideString): UTF8String;
var
  L: Integer;
  Temp: UTF8String;
begin
  Result := '';
  if WS = '' then Exit;
  SetLength(Temp, Length(WS) * 3); // SetLength includes space for null terminator
  L := UnicodeToUtf8(PChar(Temp), Length(Temp)+1, PWideChar(WS), Length(WS));
  if L > 0 then
    SetLength(Temp, L-1)
  else
    Temp := '';
  Result := Temp;
end;


function Encode2Utf8(const WS: UTF8String): WideString;
var
  L: Integer;
  Temp: WideString;
begin
  Result := '';
  if WS = '' then Exit;
  SetLength(Temp, Length(WS) * 3); // SetLength includes space for null terminator
  L := Utf8ToUnicode(PWideChar(Temp), PChar(WS), Length(WS));
  if L > 0 then
    SetLength(Temp, L-1)
  else
    Temp := '';
  Result := Temp;
end;