How Can I Precisely Identify a File's Encoding Using Byte Order Marks (BOMs)?

Use Byte Order Mark (BOM) to accurately identify file encoding

The

StreamReader.CurrentEncoding method does not always reliably provide file encoding information, and analyzing a file's byte order mark (BOM) is an accurate and efficient way to identify the encoding. The BOM sequence (if present) can indicate the encoding format.

The following code snippet introduces a method called GetEncoding that determines the encoding of a text file based on the file's BOM. If BOM detection fails, defaults to ASCII:

public static Encoding GetEncoding(string filename)
{
    // 读取 BOM
    var bom = new byte[4];
    using (var file = new FileStream(filename, FileMode.Open, FileAccess.Read))
    {
        file.Read(bom, 0, 4);
    }

    // 分析 BOM
    if (bom[0] == 0x2b && bom[1] == 0x2f && bom[2] == 0x76) return Encoding.UTF7;
    if (bom[0] == 0xef && bom[1] == 0xbb && bom[2] == 0xbf) return Encoding.UTF8;
    if (bom[0] == 0xff && bom[1] == 0xfe && bom[2] == 0 && bom[3] == 0) return Encoding.UTF32; //UTF-32LE
    if (bom[0] == 0xff && bom[1] == 0xfe) return Encoding.Unicode; //UTF-16LE
    if (bom[0] == 0xfe && bom[1] == 0xff) return Encoding.BigEndianUnicode; //UTF-16BE
    if (bom[0] == 0 && bom[1] == 0 && bom[2] == 0xfe && bom[3] == 0xff) return new UTF32Encoding(true, true);  //UTF-32BE

    // BOM 检测失败时，默认为 ASCII
    return Encoding.ASCII;
}

Using this method, you can accurately identify the encoding of a file, allowing for accurate text interpretation and manipulation.

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