Re: std::wstringbuf and imbue to convert from utf-8 to wchar_t?
On Nov 2, 8:27 pm, Boris Du?ek <boris.du...@gmail.com> wrote:
I have an API that returns UTF-8 encoded strings. I have a
utf8 codevt facet available to do the conversion from UTF-8 to
wchar_t encoding defined by the platform. I have no trouble
converting when a UTF-8 encoded string comes from file - I
just create a std::wifstream and imbue it with a locale that
uses the utf-8 facet for std::locale::ctype. Then I just use
operator>> to get wstring properly decoded from UTF-8. I
thought I could create something similar for
std::wstringstream or std::wstringbuf, but I have a hard time
with it.
It won't work, because wstringbuf doesn't take input or generate
output in the form of char's. wstringbuf uses a wstring. The
code translation in wfilebuf takes place in the wfilebuf, not in
any of the base classes, and it takes place because all file IO
in C++ involves char's; it's there to allow you to transfer
char's to and from the disk, while only seeing wchar_t at the
interface with the class.
I imagine the situation that if a std::wstringstream is imbued
with UTF-8, then it stored an array of char (not wchar_t)
which is encoded with UTF-8. I can push to it or get from it
wide string like I like, and the result is encoded in UTF-8 in
some internal buffer.
What I now need is to be able to supply my UTF-8 buffer
prefilled with the values I need in UTF-8 to act as the
internal UTF-8 encoded buffer for the std::wstingbuf, and then
call operator>>(..., std::wstring &), to get the wide-string
representation converted from the UTF-8 to the proper wide
encoding. Also while I am at it, I would like to know the
reverse - how to get this internal UTF-8 encoded buffer (so I
can push wstrings into it as I like and get a "char *" encoded
in UTF-8).
Sample code (how I would imagine it):
char name[] = "Boris Du" "\xc5\xa1" "ek"; // my name - Boris Du?ek
std::wstringstream conv;
conv.rdbuf()->pubsetcharbuf(name, 11); // pubsetbuf only accepts
"wchar_t *", not "char *"
There is no pubsetcharbuf function. It's the str() function
you'd be interested in. But in all cases; the character type of
a wstringbuf is always wchar_t; the class does not support
conversion to any other basic type. (That is, in a way, the
price we pay for it being a template.)
--
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