/**
* @brief std::string → std::wstring変換
*
* @param[out] dst 変換結果バッファ
* @param src 変換するマルチバイト文字列
* @param loc 変換に使用するlocale
* @param cvt 変換関数を提供するcodecvt
*/
void ToWideString(wstring &dst, const string &src, const codecvt<wstring::value_type, string::value_type, mbstate_t>& cvt)
{
typedef wstring::value_type wchar_type;
typedef string::value_type char_type;
typedef codecvt<wchar_type, char_type, mbstate_t> cvt_type;
size_t len = src.length();
wchar_type * buff = new wchar_type[len*2];
const char_type* const pbegin = src.c_str();
const char_type* const pend = pbegin + src.length();
const char_type* pnext = pbegin;
wchar_type* const pwbegin = &buff[0];
wchar_type* const pwend = &buff[len*2];
wchar_type* pwnext = pwbegin;
dst.clear();
mbstate_t state(0);
for(;;){
cvt_type::result result = cvt.in(state, pbegin, pend, pnext, pwbegin, pwend, pwnext);
dst.append(pwbegin, pwnext - pwbegin);
if(result == cvt_type::ok) {
break;
}
assert(result == cvt_type::error);
}
delete[] buff;
}
// A version of from_8_bit which does not use functional object, for
// performance comparison.
std::wstring from_8_bit_2(const std::string& s,
const codecvt<wchar_t, char, mbstate_t>& cvt)
{
std::wstring result;
std::mbstate_t state = std::mbstate_t();
const char* from = s.data();
const char* from_end = s.data() + s.size();
// The interace of cvt is not really iterator-like, and it's
// not possible the tell the required output size without the conversion.
// All we can is convert data by pieces.
while(from != from_end) {
// std::basic_string does not provide non-const pointers to the data,
// so converting directly into string is not possible.
wchar_t buffer[32];
wchar_t* to_next = buffer;
// Try to convert remaining input.
std::codecvt_base::result r =
cvt.in(state, from, from_end, from, buffer, buffer + 32, to_next);
if (r == std::codecvt_base::error)
throw logic_error("character conversion failed");
// 'partial' is not an error, it just means not all source characters
// we converted. However, we need to check that at least one new target
// character was produced. If not, it means the source data is
// incomplete, and since we don't have extra data to add to source, it's
// error.
if (to_next == buffer)
throw logic_error("character conversion failed");
// Add converted characters
result.append(buffer, to_next);
}
return result;
}