algorithm - How Can I Best Guess the Encoding when the BOM (Byte Order Mark) is Missing?

Question

My program has to read files that use various encodings. They may be ANSI, UTF-8 or UTF-16 (big or little endian).

When the BOM (Byte Order Mark) is there, I have no problem. I know if the file is UTF-8 or UTF-16 BE or LE.

I wanted to assume when there was no BOM that the file was ANSI. But I have found that the files I am dealing with often are missing their BOM. Therefore no BOM may mean that the file is ANSI, UTF-8, UTF-16 BE or LE.

When the file has no BOM, what would be the best way to scan some of the file and most accurately guess the type of encoding? I'd like to be right close to 100% of the time if the file is ANSI and in the high 90's if it is a UTF format.

I'm looking for a generic algorithmic way to determine this. But I actually use Delphi 2009 which knows Unicode and has a TEncoding class, so something specific to that would be a bonus.

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Answer:

ShreevatsaR's answer led me to search on Google for "universal encoding detector delphi" which surprised me in having this post listed in #1 position after being alive for only about 45 minutes! That is fast googlebotting!! And also amazing that Stackoverflow gets into 1st place so quickly.

The 2nd entry in Google was a blog entry by Fred Eaker on Character encoding detection that listed algorithms in various languages.

I found the mention of Delphi on that page, and it led me straight to the Free OpenSource ChsDet Charset Detector at SourceForge written in Delphi and based on Mozilla's i18n component.

Fantastic! Thank you all those who answered (all +1), thank you ShreevatsaR, and thank you again Stackoverflow, for helping me find my answer in less than an hour!

Answer 1

Maybe you can shell out to a Python script that uses Chardet: Universal Encoding Detector. It is a reimplementation of the character encoding detection that used by Firefox, and is used by many different applications. Useful links: Mozilla's code, research paper it was based on (ironically, my Firefox fails to correctly detect the encoding of that page), short explanation, detailed explanation.