How do I detect file encoding?

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I need to open an existing file and write to it. The file may or may not be Unicode. Is there a way to detect the encoding so that I do not alter it when I write to it? For info, I am using _wfopen_s() to open the file.

Only append mode seems to retain the exiting encoding but I need to replace the contents of the file.

I guess I could open the file for binary and check the BOM but is there an easier/better way?

Thanks.

What I have tried:

Using append mode but I need to overwrite

Posted 19-Jan-17 5:53am

softwaremonkey

Updated 19-Jan-17 6:40am

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Jochen Arndt · Accepted Answer · 2017-01-19T06:16:00

UTF-16 encoded files should always contain a Byte order mark - Wikipedia[^]. With UTF-8 files this is optional.

So you should check first for a BOM. If there is none, you might check for valid UTF-8.

With Windows you can use the MultiByteToWideChar function (Windows)[^] to do that (it must be probably called anyway to convert UTF-8 text to UTF-16 which is used by Windows).

Another option is using the ICU converter library (Using Converters - ICU User Guide[^]).

There are also some projects providing converters and check functions like UTF8-CPP: UTF-8 with C++ in a Portable Way[^].

Or write your own according to the allowed code points. I once found a sample implementation based on the Unicode recommendations but I did not find it anymore.

Note that all checks will return true (valid UTF-8) for plain ASCII files. So it might be necessary to check first for characters >= 0x80.

Richard MacCutchan · Accepted Answer · 2017-01-19T06:40:00

Solution 2

See Handling simple text files in C/C++[^]. It shows how you can identify the encoding from the first few bytes of the file.

Posted 19-Jan-17 6:40am

Richard MacCutchan