Why does wide file-stream in C++ narrow written data by default?

Question

Honestly, I just don\'t get the following design decision in C++ Standard library. When writing wide characters to a file, the wofstream converts wchar_t<

Answer 1

For your first question, this is my guess.

The IOStreams library was constructed under a couple of premises regarding encodings. For converting between Unicode and other not so usual encodings, for example, it's assumed that.

• Inside your program, you should use a (fixed-width) wide-character encoding.
• Only external storage should use (variable-width) multibyte encodings.

I believe that is the reason for the existence of the two template specializations of std::codecvt. One that maps between char types (maybe you're simply working with ASCII) and another that maps between wchar_t (internal to your program) and char (external devices). So whenever you need to perform a conversion to a multibyte encoding you should do it byte-by-byte. Notice that you can write a facet that handles encoding state when you read/write each byte from/to the multibyte encoding.

Thinking this way the behavior of the C++ standard is understandable. After all, you're using wide-character ASCII encoded (assuming this is the default on your platform and you did not switch locales) strings. The "natural" conversion would be to convert each wide-character ASCII character to a ordinary (in this case, one char) ASCII character. (The conversion exists and is straightforward.)

By the way, I'm not sure if you know, but you can avoid this by creating a facet that returns noconv for the conversions. Then, you would have your file with wide-characters.