Contributed by Anonymous Monk
on Nov 12, 2000 at 15:19 UTC
Q&A
> arrays
Answer: How do I test if an array is empty or not?
contributed by merlyn The name of the array (like @a) in a scalar context yields the number of elements currently in the array. And a boolean test selects scalar context automatically, so something like:
if (@a) { # @a is not empty...
...
} else { # @a is empty
...
}
should work just fine. | Answer: How do I test if an array is empty or not?
contributed by Fastolfe As a supplement to merlyn's answer, never be tempted to use defined on an array (or a hash for that matter). Simply testing the value of the @array in a scalar context is sufficient. The defined function makes little sense on any data type other than a $scalar. | Answer: How do I test if an array is empty or not?
contributed by quidity The answer here does depend a little bit on what you mean by 'empty'. The earlier answers only tell you if an array has any elements, but not tell you what they contain.
If by empty you mean 'only contains defined elements' then you will need the following test instead:
my @a = (0,1,2,3);
foreach (@a) {print "'$_'\n";} # Prints each element.
print "\@a exists\n" if @a;
print "\@a is not Empty\n" if grep {defined($_)} @a;
# Prints '@a is not empty' if any element in '@a' is defined.
my @b = (1, undef)
foreach (@b) {print "'$_'\n";}
print "\@b exists\n" if @b;
print "@b is not Empty\n" if grep {defined($_)} @b;
Of course, if you want to know if the array contains only true values, then you can get away without using the defined() bit.
Edited: Examples reworked by davido. | Answer: How do I test if an array is empty or not?
contributed by rajib my $j = 0;
for (my $i = 0; $i <= $#array; ++$i) {
$current = $array[$i];
if($current == undef) {
push @empty, $j++;
}
}
print "undefined indices: @empty \n";
or to put it in common perl terms
my @empties = ();
for my $i(0..$#array) {
unless(defined $array[$i]) {
push @empties, $i;
}
}
print "undefined indices @empties\n";
{Editor's note: This example doesn't work as the poster thought it would. See Abigail-II's explanation here: Re: Answer: How do I test if an array is empty or not?.}
Edited by davido for clarification.
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