basic_string< TargetChar > convert( const basic_string< SourceChar > &sourceString,
size_t ( *convertFunction )( TargetChar *dst, const SourceChar **src, size_t len, mbstate_t *state )) {
constexpr auto LENGTH_ERROR = static_cast< size_t >( -1 );
mbstate_t state = mbstate_t();
// Find out how much space we need:
const SourceChar *sourceStringData = sourceString.data();
size_t expectedTargetStringLength = convertFunction( nullptr, &sourceStringData, sourceString.length(), &state );
if ( expectedTargetStringLength == LENGTH_ERROR )
throw make_errno_system_error();
// Convert the string:
basic_string< TargetChar > targetString( expectedTargetStringLength, TargetChar() );
size_t actualTargetStringLength = convertFunction( &targetString[ 0 ], &sourceStringData, sourceString.length(), &state );
if ( actualTargetStringLength == LENGTH_ERROR )
throw make_errno_system_error();
// Could all characters be converted?
if ( expectedTargetStringLength != actualTargetStringLength )
throw system_error( make_error_code( errc::illegal_byte_sequence ));
return targetString;
}
TargetChar cast_char(SourceChar ch)
{
if (is_signed<TargetChar>::value != is_signed<SourceChar>::value)
{
if (is_signed<SourceChar>::value)
{
// source is signed, target is unsigned
typedef typename make_unsigned<SourceChar>::type USourceChar;
return TargetChar(USourceChar(ch));
}
else
{
// source is unsigned, target is signed
typedef typename make_signed<SourceChar>::type SSourceChar;
return TargetChar(SSourceChar(ch));
}
}
else
{
// source and target has same signedness
return TargetChar(ch); // just cast
}
}
