delphi获取文件编码

//delphi获取文件编码
unit EncodeUnit;

interface

uses
SysUtils, Windows, Classes;

type
TTextFormat = ( tfAnsi, tfUnicode, tfUnicodeBigEndian, tfUtf8 );

const
TextFormatFlag: array [tfAnsi..tfUtf8] of Word = ( $0000,$FFFE,$FEFF,$EFBB );

function GetFileEncodeing(const FileName: string): TTextFormat;
function WideStringToString(const WS: WideString; CodePage: Word): string;

implementation

//高低字节互换
function WordLoHiExchange(w: Word): Word; register;
asm
XCHG AL, AH
end;

//取得文件编码
function GetFileEncodeing(const FileName: string): TTextFormat;
var
W: Word;
begin
try
with TFileStream.Create(FileName,fmOpenRead or fmShareDenyNone) do
begin
Seek(0, soFromBeginning);
Read(W,2);
W := WordLoHiExchange(W); //因为是以Word数据类型读取，故高低字节互换
if W=TextFormatFlag[tfUnicode] then
Result := tfUnicode
else if W=TextFormatFlag[tfUnicodeBigEndian] then
Result := tfUnicodeBigEndian
else if W=TextFormatFlag[tfUtf8] then
Result := tfUtf8
else
Result := tfAnsi;
Free;
end;
except
Result := tfAnsi;
end;
end;

//Unicode 转 ANSI
function WideStringToString(const WS: WideString; CodePage: Word): string;
var
InputLength, OutputLength: Integer;
begin
InputLength := Length(WS);
OutputLength := WideCharToMultiByte(CodePage, 0, PWideChar(WS), InputLength, nil, 0, nil, nil);
SetLength(Result, OutputLength);
WideCharToMultiByte(CodePage, 0, PWideChar(WS), InputLength, PAnsiChar(Result), OutputLength, nil, nil);
end;

end.