error_char

ec = Encoding::Converter.new("ISO-8859-1", "EUC-JP")
begin
  ec.convert("\xa0")
rescue Encoding::UndefinedConversionError
  puts $!.error_char.dump   #=> "\xC2\xA0"
  p $!.error_char.encoding  #=> #<Encoding:UTF-8>
end