Problems iterating over array

Question

I tried writing a subroutine that iterates through a list of strings and prints each string, but it doesn't work:

use HTTP::Date;

my @date_strings_array = ("Jun 1, 2026", "Aug 26, 2018 GMT-05:00", "Aug 26, 2018");
print_datetimes(@date_strings_array);

sub print_datetimes {
    my @date_string_array = shift;

    foreach $date_string (@date_string_array) {
       print("The current iteration is $date_string.");  
    }
 }

It only prints the first iteration:

$ perl /example/test.pl
The current iteration is Jun 1, 2026.

Why does this only print the first item in the array?

choroba · Accepted Answer · 2018-06-19 15:33:13Z

3

shift only retrieves one element. You can assign the whole argument array, though:

my @date_string_array = @_;
for my $date_string (@date_string_array) {
    ...

answered Jun 19, 2018 at 15:33

choroba

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5 Comments

alex Over a year ago

Wow - that's quite irritating. This works - thanks! :)

choroba Over a year ago

Irritating? I almost always use my ($self, $whatever) = @_ instead of shifting @_.

alex Over a year ago

I mean that your answer makes sense and is elegant. But as a language feature, the syntactic differences between shift and @_ are very dramatic. It's very non-intuitive to me.

Dave Cross Over a year ago

It's not "differences between shift and @_" as both versions deal with @_ (shift() acts on @_ if given no other argument). The difference is between shift() (which removes a single element from the start of an array) and list assignment (which copies all values from the list on the right hand side ot the operator into variables on the left hand side of the operator).

Dave Cross Over a year ago

You could, of course, do this without your @date_string_array variable. foreach my $date_string (@_) { print ... } or even just print "... $_" for @_

Andrey · Accepted Answer · 2018-06-19 15:31:33Z

1

You need to pass the refenrece to array.

my @date_strings_array = ("Jun 1, 2026", "Aug 26, 2018 GMT-05:00", "Aug 26, 2018");
print_datetimes(\@date_strings_array);

sub print_datetimes {
    my $date_string_array = shift;

    foreach my $date_string (@$date_string_array) {
       print "The current iteration is $date_string.\n";  
    }
 }

answered Jun 19, 2018 at 15:31

Andrey

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1 Comment

Andrey Over a year ago

You might want to consider switching to passing array references and to @_ as choroba has suggested. Next time you may want to pass two arrays, and print them separately.

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