Re: [Boost-users] std::string to std::wstring

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2007-01-27 12:15:10

Gottlob Frege wrote:
> 
> 
> On 1/22/07, *Tobias Schwinger* <tschwinger_at_[hidden] 
> <mailto:tschwinger_at_[hidden]>> wrote:
> 
>     John Christopher wrote:
>      > Hello,
>      > Does Boost contain facilities to convert std::string into
>     std::wstring and
>      > the other way around?
> 
>     Should there?
> 
>          std::string  a;
>          std::wstring b( a.begin(),a.end());
>          std::string  c(b.begin(),b.end());
> 
>     All string algorithms in Boost are templates so they should work fine
>     with both std::string and std::wstring.
> 
>          http://www.boost.org/doc/html/string_algo.html
> 
>     Regards,
>     Tobias
> 
> 
> 
> I think the real question is whether the OP was hoping for Unicode 
> conversions of some kind in the process.  ie what 'type' (sematically) 
> are the wchar_t's and char's?  UTF16? UTF32? (what size is the wchar_t?) 
> etc.

I'm not sure that's what the OP really wanted:

If we want to convert back and forth we are probably just using the
(compatible) ASCII subset (a typical example: COM calls).

A proper conversion to UTF-8 when narrowing the character type can be 
worse than overflow if the rest of the code can't handle UTF-8.

However, Boost.Unicode sure would be a nice addition.

> Also, does the last line:
>    std::string c(b.begin(), b.end())
> give at least a compiler warning about downconverting from wchar_t to 
> char, and thus losing bits?  

Diagnostic messages are implementation-defined. The code I posted does
not warn with gcc4 (all warnings enabled), for instance.

> (Which would be a hint that maybe you need 
> some Unicode conversion or something else.)

Yeah, like most compiler warnings, it means "know what you're doing" ;-).

Regards,
Tobias