How Can I Reliably Detect the Character Encoding of a Text File?

Detecting Character Encoding in Text Files

When working with text files, it's essential to know the character encoding used to interpret the file correctly. This article explores methods to detect the character encoding of a text file.

Limitations of BOM (Byte Order Mark)

The initial section of a text file may contain a Byte Order Mark (BOM), indicating the character encoding. However, not all encodings use BOMs, and UTF-8, a widely used encoding, often omits it. Therefore, relying solely on BOM detection is insufficient.

Alternate Detection Methods

UTF-32

• BOM: 00 00 FE FF (BE) or FF FE 00 00 (LE)
• Pattern: 00 {00-10} xx xx (BE) or xx xx {00-10} 00 (LE)

US-ASCII

• No BOM
• Lack of bytes in the 80-FF range

UTF-8

• BOM: EF BB BF
• Validating as UTF-8 is a strong indicator
• Statistical analysis for false positives

UTF-16

• BOM: FE FF (BE) or FF FE (LE)
• Surrogate pairs (D[8-B]xx D[C-F]xx)

Other

• XML: Look for encoding= declaration, default to UTF-8
• Other encodings: Statistical detection or external tools

Common Default

If standard detection methods fail and no encoding declaration is found, consider assuming ISO-8859-1 or Windows-1252. These are commonly used encodings in English-speaking environments.

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