如何获取一个文件的编码方式

System.Text.Encoding enc = null;

using (System.IO.FileStream file = new System.IO.FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read))
{
if (file.CanSeek)
{
byte[] bom = new byte[4]; // Get the byte-order mark, if there is one

file.Read(bom, 0, 4);

if(bom[0] == 0xef && bom[1] == 0xbb && bom[2] == 0xbf)
{
enc = System.Text.Encoding.UTF8;
}
else if (bom[0] == 0xff && bom[1] == 0xfe)
{
// ucs-2le, ucs-4le, and ucs-16le
enc=System.Text.Encoding.Unicode;
}
else if(bom[0] == 0xfe && bom[1] == 0xff)
{
// utf-16 and ucs-2
enc=System.Text.Encoding.BigEndianUnicode;
}
else if(bom[0] == 0 && bom[1] == 0 && bom[2] == 0xfe && bom[3] == 0xff)
{
// ucs-4
enc = System.Text.Encoding.UTF32;
}
else
{
enc = System.Text.Encoding.ASCII;
}
}
else
{
// The file cannot be randomly accessed, so you need to decide what to set the default to
// based on the data provided. If you're expecting data from a lot of older applications,
// default your encoding to Encoding.ASCII. If you're expecting data from a lot of newer
// applications, default your encoding to Encoding.Unicode. Also, since binary files are
// single byte-based, so you will want to use Encoding.ASCII, even though you'll probably
// never need to use the encoding then since the Encoding classes are really meant to get
// strings from the byte array that is the file.
enc = System.Text.Encoding.ASCII;
}
return enc;
}