[cfe-dev] [libc++] using std::wstring_convert and std::codecvt_utf16 to convert const char16_t* to wstring

[Ryan Ericson]

-Cfe-dev

I'm sorry for being impatient and asking it here again before I got
the answer =). Now that I know you (and Cubbi) are on StackOverflow,
I'll use that for questions like these. =)

Thanks!!!

On Fri, Dec 16, 2011 at 4:13 PM, Howard Hinnant <hhinnant at apple.com> wrote:
> On Dec 16, 2011, at 6:09 PM, Ryan Ericson wrote:
>
>> Hi,
>>
>> I'm learning about unicode support in C++ and I'm trying to convert
>> const char16_t* (UTF-16) to wstring (UCS4). Reading the standard (and
>> if I understand it correctly), it can be done through
>> std::codecvt_utf16:
>>
>> "For the facet codecvt_utf16:
>> — The facet shall convert between UTF-16 multibyte sequences and UCS2
>> or UCS4 (depending on thesize of Elem) within the program."
>>
>> So I tried to use std::wstring_convert to do the conversion by doing
>> the following:
>>
>> #include <iostream>
>> #include <locale>
>> #include <codecvt>
>> #include <string>
>>
>> using namespace std;
>>
>> int main()
>> {
>>     u16string s;
>>
>>     s.push_back('h');
>>     s.push_back('e');
>>     s.push_back('l');
>>     s.push_back('l');
>>     s.push_back('o');
>>
>>     wstring_convert<codecvt_utf16<wchar_t>, wchar_t> conv;
>>     wstring ws = conv.from_bytes(reinterpret_cast<const char*> (s.c_str()));
>>
>>     wcout << ws << endl;
>>
>>     return 0;
>> }
>>
>> Note: the explicit push_backs to get around the fact that my version
>> of clang (Xcode 4.2) doesn't have unicode string literals.
>>
>> When the code is run, I get terminate exception from from_bytes. Am I
>> misunderstanding something and doing something illegal here? I was
>> thinking it should work because the const char* that I passed to
>> wstring_convert is UTF-16 encoded. I have also considered endianness
>> being the issue, but I have checked that it's not the case.
>> If that is indeed not going to work, what would be the best approach
>> to convert UTF-16 to UCS4 using standard C++11?
>
> Cubbi beat me to figuring this out by 58 minutes. ;-)
>
> Howard
>