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textscan to parse string

Asked by Hugo SP on 20 Feb 2013

Hello,

I am trying to use textscan to parse an IP address to get 4 integers:

str = '48.2.81.56'

integers = textscan(str,'%u8',4, 'Delimiter', '.');

Why is this is not working correctly?

Thank you.

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Hugo SP

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1 Answer

Answer by Walter Roberson on 20 Feb 2013
Accepted answer

Unfortunately, in at least some versions, textscan() keeps reading for numeric fields as long as what is in the input is characters that could be part of a number format. It does not pay attention to the delimiter until after it has done that.

So the 48.2.81.56 is read as "4 is a digit, 8 is a digit, decimal place is part of a floating point format, 2 is a digit, decimal point has already occurred in the number so the number must have ended, 48.2; now look, the decimal point is the delimiter. Okay 8 and 1 are digits, decimal point is part of a floating point format, 5 and 6 are digits, end of string so the number has ended, 81.56. Now convert the 48.2 and 81.56 into the %u8 format."

What you should do instead is

integers = uint8( str2double( regexp( str, '\.', 'split' ) ) )

4 Comments

Walter Roberson on 20 Feb 2013

Yes, that is an alternative to 'split'; the str2double() and uint8() would still be needed around it, of course.

Hugo SP on 20 Feb 2013

Thank you for the answer. However, I think that this is a bug and should be corrected. I don't understand how '.' is part of an integer format, which is what I requested. If it was %f I would understand the error.

Walter Roberson on 20 Feb 2013

Please submit a bug report; I do not work for Mathworks.

Walter Roberson

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