C#实现获取文本文件的编码的一个类（区分GB2312和UTF8）

以下是获取文件编码的一个类：

using system;
using system.io;
using system.text;
 
/// <summary>
/// fileencoding 的摘要说明
/// </summary>
namespace fileencoding
{
/// <summary>
/// 获取文件的编码格式
/// </summary>
public class encodingtype
{
/// <summary>
/// 给定文件的路径，读取文件的二进制数据，判断文件的编码类型
/// </summary>
/// <param name="file_name">文件路径</param>
/// <returns>文件的编码类型</returns>
public static system.text.encoding gettype(string file_name)
{
filestream fs = new filestream(file_name, filemode.open, fileaccess.read);
encoding r = gettype(fs);
fs.close();
return r;
}
 
/// <summary>
/// 通过给定的文件流，判断文件的编码类型
/// </summary>
/// <param name="fs">文件流</param>
/// <returns>文件的编码类型</returns>
public static system.text.encoding gettype(filestream fs)
{
byte[] unicode = new byte[] { 0xff, 0xfe, 0x41 };
byte[] unicodebig = new byte[] { 0xfe, 0xff, 0x00 };
byte[] utf8 = new byte[] { 0xef, 0xbb, 0xbf }; //带bom
encoding reval = encoding.default;
 
binaryreader r = new binaryreader(fs, system.text.encoding.default);
int i;
int.tryparse(fs.length.tostring(), out i);
byte[] ss = r.readbytes(i);
if (isutf8bytes(ss) || (ss[0] == 0xef && ss[1] == 0xbb && ss[2] == 0xbf))
{
reval = encoding.utf8;
}
else if (ss[0] == 0xfe && ss[1] == 0xff && ss[2] == 0x00)
{
reval = encoding.bigendianunicode;
}
else if (ss[0] == 0xff && ss[1] == 0xfe && ss[2] == 0x41)
{
reval = encoding.unicode;
}
r.close();
return reval;
 
}
 
/// <summary>
/// 判断是否是不带 bom 的 utf8 格式
/// </summary>
/// <param name="data"></param>
/// <returns></returns>
private static bool isutf8bytes(byte[] data)
{
int charbytecounter = 1; //计算当前正分析的字符应还有的字节数
byte curbyte; //当前分析的字节.
for (int i = 0; i < data.length; i++)
{
curbyte = data[i];
if (charbytecounter == 1)
{
if (curbyte >= 0x80)
{
//判断当前
while (((curbyte <<= 1) & 0x80) != 0)
{
charbytecounter++;
}
//标记位首位若为非0 则至少以2个1开始 如:110xxxxx...........1111110x 
if (charbytecounter == 1 || charbytecounter > 6)
{
return false;
}
}
}
else
{
//若是utf-8 此时第一位必须为1
if ((curbyte & 0xc0) != 0x80)
{
return false;
}
charbytecounter--;
}
}
if (charbytecounter > 1)
{
throw new exception("非预期的byte格式");
}
return true;
}
 
}
 
 
}

以下是使用示例：

#region 打开按钮
/// <summary>
/// 打开按钮
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void txtmenuopen_click(object sender, eventargs e)
{
string fname;
openfiledialog openfiledialog = new openfiledialog();
openfiledialog.initialdirectory = "";//注意这里写路径时要用c:而不是c: 
openfiledialog.filter = "文本文档|*.txt";
openfiledialog.restoredirectory = true;
openfiledialog.filterindex = 1;
if (openfiledialog.showdialog() == dialogresult.ok)
{
fname = openfiledialog.filename;
 
txtbox.text = system.io.file.readalltext(fname,
fileencoding.encodingtype.gettype(fname));
} 
 
}
#endregion