How Can I Precisely Determine a File's Encoding Using its Byte Order Mark (BOM)?

Utilize Byte Order Mark (BOM) to accurately determine file encoding

Accurately determining file encoding is critical to ensuring data accuracy and compatibility across platforms. This can be challenging, especially with obscure or unreliable methods like Notepad.

A highly accurate way to identify a file's encoding is to analyze the file's Byte Order Mark (BOM). The BOM is a specific sequence of bytes that indicates the encoding of a text file.

Using a programming language, we can get the BOM from a text file and analyze it to determine its encoding. If the file has a BOM, this method can accurately identify the encoding. For example, the following C# code:

<code class="language-csharp">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

    // 如果未找到 BOM，则默认为 ASCII
    return Encoding.ASCII;
}</code>

This method provides a clear and concise way to accurately determine the file encoding based on the BOM, and is a reliable alternative to unreliable methods such as StreamReader.CurrentEncoding.

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