C++ unicode file io

Question

I need a file io library that can give my program a utf-16 (little endian) interface, but can handle files in other encodings, mainly ascii(input only), utf-8, utf-16, utf-32/ucs4 including both little and big endian byte orders.

Having looked around the only library I found was the ICU ustdio.h library.

I did try it however I coudlnt even get that to work with a very simple bit of text, and there is pretty much zero documentation on its useage, only the ICU file reference page which providse no examples and very little detail (eg having made a UFILE from an existing FILE, is it safe to use other functions that take the FILE*? along with several others...).

Also id far rather a c++ library that can give me a wide stream interface over a C style interface...

std::wstring str = L"Hello World in UTF-16!\nAnother line.\n";
UFILE *ufile = u_fopen("out2.txt", "w", 0, "utf-16");
u_file_write(str.c_str(), str.size(), ufile);
u_fclose(ufile);

output

Hello World in UTF-16!਍䄀渀漀琀栀攀爀 氀椀渀攀⸀ഀ

hex

FF FE 48 00 65 00 6C 00 6C 00 6F 00 20 00 57 00
6F 00 72 00 6C 00 64 00 20 00 69 00 6E 00 20 00
55 00 54 00 46 00 2D 00 31 00 36 00 21 00 0D 0A
00 41 00 6E 00 6F 00 74 00 68 00 65 00 72 00 20
00 6C 00 69 00 6E 00 65 00 2E 00 0D 0A 00

EDIT: The correct output on windows would be:

FF FE 48 00 65 00 6C 00 6C 00 6F 00 20 00 57 00 
6F 00 72 00 6C 00 64 00 20 00 69 00 6E 00 20 00 
55 00 54 00 46 00 2D 00 31 00 36 00 21 00 0D 00 
0A 00 41 00 6E 00 6F 00 74 00 68 00 65 00 72 00
20 00 6C 00 69 00 6E 00 65 00 2E 00 0D 00 0A 00

Answer 1

The problem you see comes from the linefeed conversion. Sadly, it is made at the byte level (after the code conversion) and is not aware of the encoding. IOWs, you have to disable the automatic conversion (by opening the file in binary mode, with the "b" flag) and, if you want 0A00 to be expanded to 0D00A00, you'll have to do it yourself.

You mention that you'd prefer a C++ wide-stream interface, so I'll outline what I did to achieve that in our software:

• Write a std::codecvt facet using an ICU UConverter to perform the conversions.
• Use an std::wfstream to open the file
• imbue() your custom codecvt in the wfstream
• Open the wfstream with the binary flag, to turn off the automatic (and erroneous) linefeed conversion.
• Write a "WNewlineFilter" to perform linefeed conversion on wchars. Use inspiration from boost::iostreams::newline_filter
• Use a boost::iostreams::filtering_wstream to tie the wfstream and the WNewlineFilter together as a stream.

Answer 2

I successfully worked with the EZUTF library posted on CodeProject: High Performance Unicode Text File I/O Routines for C++