Boost C++ Libraries: Ticket #7929: boost::lexical_cast< std::string, std::wstring > gives a compiler error.

owner, component changed; cc set

Antony Polukhin — Mon, 28 Jan 2013 18:48:09 GMT

cc antoshkka@… added
owner changed from Antony Polukhin to Vladimir Prus
component lexical_cast → program_options

I'm afraid that this is not a bug of lexical_cast. Lexical_cast shall work like a std::stringstream/std::wstringstream, so the first example is equal to the following:

#include <sstream>
int main() {
    std::wstringstream wss(L"some string");
    std::string str;
    wss >> str;  // Compilation error
    return 0;
}

And this code must not compile (if I'm wrong and my current compiler fail to compile a correct code - please tell me about it).

So, this looks more like a program_options bug.

nate@… — Tue, 29 Jan 2013 06:29:22 GMT

I'm not sure I agree that lexical_cast is just supposed to be a wrapper around std::stringstream when its own documentation states:

The lexical_cast function template offers a convenient and consistent form for supporting common conversions to and from arbitrary types when they are represented as text.

That, to me, sounds like it should work for converting std::wstring to std::string. It is an common conversion dealing with arbitrary types and text.

Antony Polukhin — Fri, 01 Feb 2013 14:00:24 GMT

To be honest, I also miss that functionality sometimes.

But before implementing it, I need to

fix existing issues with std::locale on some compilers
determinate a portable and reliable way to do narrowing of characters (it looks almost impossible to me)

So this won't be fixed in nearest future. And I'm afraid that Boost.Locale shall be used in such cases...

nate@… — Wed, 12 Jun 2013 19:07:09 GMT

Perhaps one can look to the standard library for inspiration? In the locale header there is the std::codecvt class which can be used with std::wstring_convert to perform convertions from one encoding to another.

Below is an example using the C++11 class std::codecvt_utf8_utf16 to convert a UTF-16 std::wstring to a UTF-8 encoded std::string. I am using this in my application to great success so far.

    std::wstring wideString;
    std::wstring_convert<
        std::codecvt_utf8_utf16< std::wstring::value_type >,
        std::wstring::value_type
    > utf16conv;
    std::string narrowString = utf16conv.to_bytes( wideString );

I hope this helps to show a potential way to narrow characters.