The standard Perl approach to rounding numbers (with sprintf) amounts to using a string manipulation for what is arguably an arithmetic task. Did you have any particular error in mind?

When I first saw the question, the two solutions I thought of were $x - int( $x ) or indeed something along the lines of $x =~ s/\d+(?=\.)//, and I'm curious about what errors could have resulted from the latter approach.

A loss of precision:

#! perl -slw
use strict;

my $pi = 3.141592653589793238462643383279502;

print $pi - int( $pi );

( my $fract = $pi ) =~  s/\d+(?=\.)//;

print $fract;
__END__
P:\test>462902
0.141592653589793
.14159265358979
[download]

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?

"Science is about questioning the status quo. Questioning authority".

The "good enough" maybe good enough for the now, and perfection maybe unobtainable, but that should not preclude us from striving for perfection, when time, circumstance or desire allow.

Having a mental map that considers strings numbers and numbers strings allows one to make subtle errors in their programs.

In fact, sprintf returns a string after doing an arithmatic operation. Compare a 2 deciaml point operation via sprintf:


my $num = 4.62899;
$round = sprintf "%.2f", $num;
print "$round\n";
[download]


prints 4.63, which is not a trimming of the string to two decimal places.

For another example consider this snip and output.


my $string = "0.0";
print "string $string is ", ($string ? "True" : "False"), "\n";
print "string $string is ", ($string+0 ? "True" : "False"), "\n";
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Which prints:
string 0.0 is True
string 0.0 is False
Be Appropriate && Follow Your Curiosity

prints 4.63, which is not a trimming of the string to two decimal places.

That's not a bug; it's a feature :-) . Seriously, that's the documented behavior for sprintf, and precisely why it is the standard way to do rounding in Perl.

the lowliest monk