is there any way we can check if string needs decoding in utf-8.

Put more clearly, you are asking if there's a way to tell whether a string has already been decoded, or whether it's still encoded using UTF-8.

There's no way to tell for sure.

You could use something like the following: 

sub is_valid_utf8 {
   return $_[0] =~ /
      ^
      (?: [\x00-\x7F]
      |   [\xC0-\xDF] [\x80-\xBF]
      |   [\xE0-\xEF] [\x80-\xBF]{2}
      |   [\xF0-\xF7] [\x80-\xBF]{3}
      )*+
      \z
   /x
}

utf8::decode($string)
   if is_valid_utf8($string);

[download]

This simplifies to 

utf8::decode($string);

[download]

This won't always work. Certain decoded strings are valid UTF-8. That said, these strings would likely be nonsense. I think the conditions I listed here would apply. So the above is actually quite reliable.

In reply to Re: How to avoid decoding string to utf-8. by ikegami
in thread How to avoid decoding string to utf-8. by Anonymous Monk

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