Programming the Perl DBI

Numeric Testing

The final utility function supplied by DBI that we’ll look at is quite a curious one called looks_like_number() . This function quite simply tells you whether or not a value looks like a number or not.

looks_like_number() operates by taking a list of values as an argument and returns a new array signifying whether or not the corresponding value within the original array was a number, not a number, or undefined.

This may seem rather a curious thing to want to do, but in the case of handling large quantities of data, it’s useful for working out which values might need to have their quotes escaped via the quote() method.

The returned array will contain the same number of values as the original data array, with the elements containing one of three values signifying the following:

true        The original value is a number.
false       The original value is not a number.
undef       The original value is empty or undefined.

The following example illustrates how this process works:

#!/usr/bin/perl -w # # ch04/util/lookslike1: Tests out the DBI::looks_like_number() function. # use DBI; ### Declare a list of values my @values = ( 333, 'Choronzon', 'Tim', undef, 'Alligator', 1234.34, 'Linda', 0x0F, '0x0F', 'Larry Wall' ); ### Check to see which are numbers! my @areNumbers = DBI::looks_like_number( @values ); for (my $i = 0; $i < @values; ++$i ) { my $value = (defined $values[$i]) ? $values[$i] : "undef"; print "values[$i] -> $value "; if ( defined $areNumbers[$i] ) { if ( $areNumbers[$i] ) { ...