How to encode a perl array of hashes to an unnamed JSON array?

Question

I have an array of hashes that I would like to convert into an un-named JSON array.

If I have an array of hashes which I then try to encode to JSON as such:

my @labs = ();  
push (@labs, {id=>'1', title=>'Lab1'});  
push (@labs, {id=>'2', title=>'Lab2'});  
my $json_text = to_json {\@labs}, {ascii=>1, pretty => 1};

then the resulting JSON looks like:

{
   "ARRAY(0x358a18)" : null
}

when in fact I want it to look like:

[  
   {"title" : "Lab1", "id" : "1"},  
   {"title" : "Lab2", "id" : "2"}  
]

Try add a key, like array to the hash: to_json ({array => \@labs} or use as @MattJacob said: to_json \@labs, {ascii=>1, pretty => 1} — Håkon Hægland
– Håkon Hægland, Commented Oct 28, 2015 at 14:53
lose the curly braces from around \@labs - they're converting the array into an object — Alnitak
– Alnitak, Commented Oct 28, 2015 at 14:55
Please always use strict and use warnings 'all' at thje top of every Perl program you write. That code gives Odd number of elements in anonymous hash because of {\@labs} — Borodin
– Borodin, Commented Oct 28, 2015 at 14:59

Alnitak · Accepted Answer · 2015-10-28 14:58:31Z

7

Remove the curly braces from around \@labs - they're converting the array you've created into an anonymous hash before passing it to to_json:

#!/usr/bin/perl -w
use JSON -support_by_pp;
use strict;
my @labs = ();  
push (@labs, {id=>'1', title=>'Lab1'});  
push (@labs, {id=>'2', title=>'Lab2'});  
my $json_text = to_json \@labs, {ascii=>1, pretty => 1}; 
print $json_text;

output:

[
   {
      "title" : "Lab1",
      "id" : "1"
   },
   {
      "title" : "Lab2",
      "id" : "2"
   }
]

answered Oct 28, 2015 at 14:58

Alnitak

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Comments

Borodin · Accepted Answer · 2015-10-28 15:02:11Z

3

Your syntax is wrong, as you would have discovered if you had

use strict;
use warnings 'all';

at the top of your program. I must write that on Stack Overflow at least one a day, but still everyone thinks it doesn't apply to them

use strict;
use warnings 'all';
use v5.10.1;

use JSON;

my @labs;
push @labs, { id => 1, title => 'Lab1' };
push @labs, { id => 2, title => 'Lab2' };

say to_json \@labs, { ascii => 1, pretty => 1 };

output

[
   {
      "id" : 1,
      "title" : "Lab1"
   },
   {
      "id" : 2,
      "title" : "Lab2"
   }
]

answered Oct 28, 2015 at 15:02

Borodin

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5 Comments

Sobrique Over a year ago

Do we have a canonical 'why should I use strict and warnings'? I suppose it's not really appropriate to close as a dupe... (although maybe, because it is sort of 'typographic error' level of close).

Borodin Over a year ago

There's Why use strict and warnings? but I'm not very fond of the answers. There's also this from Perl Monks and this from Perl Maven. I'm not interested in what people write in their own time, but it's definitely grounds for closure if a question is posted here that doesn't have strictures and warnings in place -- it's just gratuitously wasting people's time

Borodin Over a year ago

Also this answer is a high-quality discussion of a related question

Vanyel Ashkevron Over a year ago

Thanks for the info regarding strict and warnings. I haven't touched perl in a very long time and am trying to make a few changes to an existing perl based web app. This will definitely help me to debug any issues in the future.

Borodin Over a year ago

@VanyelAshkevron: It's a little tricky if your existing code doesn't have use strict in place. In that circumstance all undeclared variables are global package variables, which would be declared with our instead of my. If you use strict and start declaring variables then you may introduce bugs. If you add use strict and get lots of Global symbol requires explicit package name (which is Perl's legacy error message for an undeclared variable) then you should probably add no strict 'vars' as well rather than trying to declare stuff. You should be fine with use warnings 'all'

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