vindaloo has asked for the wisdom of the Perl Monks concerning the following question:

Hi all, I am looking for the best way to test for a float. I am using something like this: 
my $var = 2.5;
if (int($var) != $var) {
 print "Is a float\n";
}

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It is not always working though. Is there a standard and tested way to test for a float in Perl?

Replies are listed 'Best First'.
Re: dependable way to test for a float
by davidrw (Prior) on May 04, 2005 at 23:43 UTC
    You can test with a regexp, which you can roll your own with something like (this is a fairly simple example): 
      if ( $var =~ /^-?\d+(\.\d+)?$/ ){
    # you have a float
  }

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    But I'd recommend checking out Regexp::Common::number which will cover many more cases.
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Re: dependable way to test for a float
by Thelonious (Scribe) on May 05, 2005 at 07:44 UTC 
    use Scalar::Util::Numeric qw(isfloat);

my $var = shift || 0E0;

print "'$var' is ";
print "not " unless isfloat($var);
print "a float\n";

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Re: dependable way to test for a float
by shemp (Deacon) on May 04, 2005 at 23:43 UTC
    From the perl cookbook section 2.1, with my own reformatting and comments: 
    sub isThisADecimalNumber {
    my ($string) = @_;

    return $string =~ /^\s*
                        -?              # negative sign - optional
                        (?:
                            \d+         # digits
                            (?:\.\d*)?  # and an optional decimal and 
+maybe more digits
                        |               # OR
                            \.\d+       # a decimal and some digits
                        )
                        \s*$/x;
}

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[d/l]
      An optional decimal would not be a float, so I think this is not testing for a float.
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        I see your point. My test is more to check if a string is numeric or not, not exactly is this number a float.
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Re: dependable way to test for a float
by Roy Johnson (Monsignor) on May 04, 2005 at 23:34 UTC
    When doesn't it work? What do you want to differentiate a float from?
    Caution: Contents may have been coded under pressure.
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      I have not totally isolated when it does not work yet. I am testing for a floating point number to separate from both booleans and strings all of which are values in a hash.

      I just had deja vu writing this....yet no recollection of doing this in a past life.

[reply]
        For your purposes, are the integers not floats? I can't think of any case where the int($n) != $n test wouldn't work. Or would it be a float if it were '0.0' (for example)?

        Though you haven't isolated when it doesn't work, can you give any example for which it doesn't work?

        Caution: Contents may have been coded under pressure.
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