CropCircle has asked for the wisdom of the Perl Monks concerning the following question:

Hello! I have a variable ($json), which contains some json structure, then try to write it in data_out file but get this error: malformed text data., at character offset 0 (before "HASH(0x39e290)"). Here is the code: 

use strict;
use warnings;

binmode STDOUT, ":utf8";
use utf8;

use JSON;

my $json ={
    'book' => {
        'title' => 'smth',
        'num_page' => 234
    }
};

my $data = decode_json($json);
open my $fh, ">", "data_out.json";
print $fh encode_json($data);
close $fh;

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Have no ideas how to fix it. Thanks for help!

Replies are listed 'Best First'.
Re: Write json structure to a file
by Corion (Patriarch) on Aug 13, 2015 at 11:29 UTC

    Your initial data structure in $json is a data structure and not text. So it does not make sense to call decode_json with it. Just delete that line.

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      It works now but I get data_out file with wrong order of structure fields - the first field is num_page, not title. Is it possible to make it constant?

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        No. Perl hashes have no order, so the sequence in which hash keys are serialized is more or less random.

        Update: Note that Javascript does not define an order over the properties of objects either, so there is very little guarantee that a JSON document will have the keys in a specific order. It seems that ECMAscript 6 standardizes somewhat on "insertion order".

        The JSON definition declares that

        An object is an unordered set of name/value pairs.

        So, for hashes, JSON does not specify an order of the keys.

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        If you wish it to be ordered in your output (more for human consumption), look at the JSON Documentation at the canonical option.

        Update: fixed link (Your Mother)

        --MidLifeXis

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        ++Corion, and so if you want ordered pairs (same rules for json as Perl), the most obvious treatment is to replace that hash with an array of little hashes, e.g.:
        use strict;
use warnings;

binmode STDOUT, ":utf8";
use utf8;

use JSON;

my $json ={
    'book' => [
        {'title' => 'smth'},
        {'num_page' => 234}
    ]
};
open my $fh, ">", "data_out.json";
print $fh encode_json($json);
close $fh;

        [download]
        Alternatively, you could sort the hash keys on the receiving end in Javascript into a particular order (put the key names in another hash with the sort positions as values for use in a sort function in Javascript) but that would be outside the scope of the monastery.

        One world, one people

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