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Re: Is it a number?

by princepawn (Parson)
on Nov 11, 2002 at 20:48 UTC ( #212084=note: print w/replies, xml ) Need Help??

in reply to Does it look like a number?

I remember in "Effective Perl Programming" merlyn did something like this:
$_ && bit_flip $_ eq "0"
Where bit_flip is something I forgot how to do in Perl.

Carter's compass: I know I'm on the right track when by deleting something, I'm adding functionality

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Re: Re: Is it a number?
by broquaint (Abbot) on Nov 12, 2002 at 00:19 UTC
    Ah yes, that would be
    sub is_numeric { ($_[0] & ~ $_[0]) eq "0"; }
    Which tests whether a scalar is a numeric value or a string value e.g 42 vs "42". Whereas the snippet discerns whether a given scalar looks like a number or not e.g
    print +(isnum($_) ? "is a number" : "not a number"), ": $_", $/ for qw( 1 2.2 3e3 4. .5); __output__ is a number: 1 is a number: 2.2 is a number: 3e3 is a number: 4. is a number: .5



      Yeah, the difference is the difference between "could this string be converted into a number without getting the warnings if -w is on?" vs "is this value always and only a number?". Everything in the latter case is also true for the former, but the inverse is not true. For example, all external data read from filehandles is always a string initially, so it could never pass this "is_numeric" test.

      -- Randal L. Schwartz, Perl hacker
      Be sure to read my standard disclaimer if this is a reply.

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