UTF-8字符串转为AnsiString

//江雪 2001.06.11 http://asnowcn.at.china.com
//将utf-8字符串转为代码页为codepage的ansistring。
function utf8toansistring(utf8str:string; codepage:integer):ansistring;
var
i:integer;
buffer:widestring;
ch,c1,c2:byte;
begin
result:='';
i:=1;
while i<=length(utf8str) do begin
ch:=byte(utf8str);
setlength(buffer,length(buffer)+1);
if (ch and $80)=0 then //1-byte
buffer[length(buffer)]:=widechar(ch)
else begin
if (ch and $e0) = $c0 then begin // 2-byte
inc(i);
c1 := byte(utf8str);
buffer[length(buffer)]:=widechar((word(ch and $1f) shl 6) or (c1 and $3f));
end
else begin // 3-byte
inc(i);
c1 := byte(utf8str);
inc(i);
c2 := byte(utf8str);
buffer[length(buffer)]:=widechar(
(word(ch and $0f) shl 12) or
(word(c1 and $3f) shl 6) or
(c2 and $3f));
end;
end;
inc(i);
end; //while
i := widechartomultibyte(codepage,
wc_compositecheck or wc_discardns or wc_sepchars or wc_defaultchar,
@buffer[1], -1, nil, 0, nil, nil);
if i>1 then begin
setlength(result, i-1);
widechartomultibyte(codepage,
wc_compositecheck or wc_discardns or wc_sepchars or wc_defaultchar,
@buffer[1], -1, @result[1], i-1, nil, nil);
end;
end;