c++ - Read Unicode Files

Question

I have a problem reading and using the content from unicode files.

I am working on a unicode release build, and I am trying to read the content from an unicode file, but the data has strange characters and I can't seem to find a way to convert the data to ASCII.

I'm using fgets. I tried fgetws, WideCharToMultiByte, and a lot of functions which I found in other articles and posts, but nothing worked.

Answer 1

Because you mention WideCharToMultiByte I will assume you are dealing with Windows.

"read the content from an unicode file ... find a way to convert data to ASCII"

This might be a problem. If you convert Unicode to ASCII (or other legacy code page) you will run into the risk of corrupting/losing data. Since you are "working on a unicode release build" you will want to read Unicode and stay Unicode.

So your final buffer will have to be wchar_t (or WCHAR, or CStringW, same thing).

So your file might be utf-16, or utf-8 (utf-32 is quite rare). For utf-16 the endianess might also matter. If there is a BOM that will help a lot.

Quick steps:

• open file with wopen, or _wfopen as binary
• read the first bytes to identify encoding using the BOM
• if the encoding is utf-8, read in a byte array and convert to wchar_t with WideCharToMultiByte and CP_UTF8
• if the encoding is utf-16be (big endian) read in a wchar_t array and _swab
• if the encoding is utf-16le (little endian) read in a wchar_t array and you are done

Also (if you use a newer Visual Studio), you might take advantage of an MS extension to _wfopen. It can take an encoding as part of the mode (something like _wfopen(L"newfile.txt", L"rw, ccs=<encoding>"); with the encoding being UTF-8 or UTF-16LE). It can also detect the encoding based on the BOM.

Warning: to be cross-platform is problematic, wchar_t can be 2 or 4 bytes, the conversion routines are not portable...

Useful links:

• BOM (http://unicode.org/faq/utf_bom.html)
• wfopen (http://msdn.microsoft.com/en-us/library/yeby3zcb.aspx)