{

std::basic_string<ToChar> result;

std::mbstate_t state = std::mbstate_t();

const FromChar* from = s.data();

const FromChar* from_end = s.data() + s.size();

// The interface 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.

ToChar buffer[32];

ToChar* to_next = buffer;

// Need variable because boost::bind doesn't work with rvalues.

ToChar* to_end = buffer + 32;

std::codecvt_base::result r =

fun(state, from, from_end, from, buffer, to_end, to_next);

if (r == std::codecvt_base::error)

boost::throw_exception(

std::logic_error("character conversion failed"));

// 'partial' is not an error, it just means not all source

// characters were 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)

boost::throw_exception(

std::logic_error("character conversion failed"));

// Add converted characters

result.append(buffer, to_next);

}

return result;