Does wide character input/output in C always read from / write to the correct (system default) encoding?

Question

I\'m primarily interested in the Unix-like systems (e.g., portable POSIX) as it seems like Windows does strange things for wide characters.

Do the read and write wid

Answer 1

The relevant text governing the behavior of the wide character stdio functions and their relationship to locale is from POSIX XSH 2.5.2 Stream Orientation and Encoding Rules:

http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_05_02

Basically, the wide character stdio functions always write in the encoding that's in effect (per the LC_CTYPE locale category) at the time the FILE stream becomes wide-oriented; this means the first time a wide stdio function is called on it, or fwide is used to set the orientation to wide. So as long as a proper LC_CTYPE locale is in effect matching the desired "system" encoding (e.g. UTF-8) when you start working with the stream, everything should be fine.

However, one important consideration you should not overlook is that you must not mix byte and wide oriented operations on the same FILE stream. Failure to observe this rule is not a reportable error; it simply results in undefined behavior. As a good deal of library code assumes stderr is byte oriented (and some even makes the same assumption about stdout), I would strongly discourage ever using wide-oriented functions on the standard streams. If you do, you need to be very careful about which library functions you use.

Really, I can't think of any reason at all to use wide-oriented functions. fprintf is perfectly capable of sending wide-character strings to byte-oriented FILE streams using the %ls specifier.