C ++中的便携式wchar_t

Question

Is there a portable wchar_t in C++? On Windows, its 2 bytes. On everything else is 4 bytes. I would like to use wstring in my application, but this will cause problems if I decide down the line to port it.

Answer 1

If you're dealing with use internal to the program, don't worry about it; a wchar_t in class A is the same as in class B.

If you're planning to transfer data between Windows and Linux/MacOSX versions, you've got more than wchar_t to worry about, and you need to come up with means to handle all the details.

You could define a type that you'll define to be four bytes everywhere, and implement your own strings, etc. (since most text handling in C++ is templated), but I don't know how well that would work for your needs.

Something like typedef int my_char; typedef std::basic_string<my_char> my_string; typedef int my_char; typedef std::basic_string<my_char> my_string;

Answer 2

What do you mean by "portable wchar_t"? There is a uint16_t type that is 16bits wide everywhere, which is often available. But that of course doesn't make up a string yet. A string has to know of its encoding to make sense of functions like length() , substring() and so on (so it doesn't cut characters in the middle of a code point when using utf8 or 16). There are some unicode compatible string classes i know of that you can use. All can be used in commercial programs for free (the Qt one will be compatible with commercial programs for free in a couple of months, when Qt 4.5 is released).

ustring from the gtkmm project. If you program with gtkmm or use glibmm, that should be the first choice, it uses utf-8 internally. Qt also has a string class, called QString. It's encoded in utf-16 . ICU is another project that creates portable unicode string classes, and has a UnicodeString class that internally seems to be encoded in utf-16, like Qt. Haven't used that one though.

Answer 3

The proposed C++0x standard will have char16_t and char32_t types. Until then, you'll have to fall back on using integers for the non- wchar_t character type.

#if defined(__STDC_ISO_10646__)
    #define WCHAR_IS_UTF32
#elif defined(_WIN32) || defined(_WIN64)
    #define WCHAR_IS_UTF16
#endif

#if defined(__STDC_UTF_16__)
    typedef _Char16_t CHAR16;
#elif defined(WCHAR_IS_UTF16)
    typedef wchar_t CHAR16;
#else
    typedef uint16_t CHAR16;
#endif

#if defined(__STDC_UTF_32__)
    typedef _Char32_t CHAR32;
#elif defined(WCHAR_IS_UTF32)
    typedef wchar_t CHAR32;
#else
    typedef uint32_t CHAR32;
#endif

According to the standard, you'll need to specialize char_traits for the integer types. But on Visual Studio 2005, I've gotten away with std::basic_string<CHAR32> with no special handling.

I plan to use a SQLite database.

Then you'll need to use UTF-16, not wchar_t .

The SQLite API also has a UTF-8 version. You may want to use that instead of dealing with the wchar_t differences.

Answer 4

My suggestion. Use UTF-8 and std::string. Wide strings would not bring you too much added value. As you anyway can't interpret wide character as letter as some characters crated from several unicode code points.

So use anywhere UTF-8 and use good library to deal with natural languages. Like for example Boost.Locale.

Bad idea: define something like typedef uint32_t mychar; is bad. As you can't use iostream with it, you can't create for example stringstream based in this character as you would not be able to write in it.

For example this would not work:

std::basic_ostringstream<unsigned> s;
ss << 10;

Would not create you a string.