在Perl中解码和使用JSON数据

my $json_raw = getJSON(); 
my $content  = decode_json($json_raw);
print Data::Dumper($content);

$VAR1 = { 'items' => [ 1,2,3,4 ] };

$content{'items'}[0]

$content->{items}[0]

初学者对初学者的回答:)当然不是应该如此专业,但也许可以帮助你.

use strict;    #use this all times
use warnings;  #this too - helps a lot!
use JSON;

my $json_str = '    { "items" : [ 1,4 ] }    ';
my $content = decode_json($json_str);

你写了：

My guess tells me that,once decoded,the object will be a hash with
one element that has the key items and an array reference as the value.

是的,它是一个散列,但是decode_json返回一个引用,在本例中是对hash的引用. (来自文档)

expects an UTF-8 (binary) string and tries to parse that
as an UTF-8 encoded JSON text,
returning the resulting reference.

在线

my $content = decode_json($json_str);

您分配给SCALAR变量(不是哈希).

因为你知道：它是一个参考,你可以做下一个：

printf "reftype:%sn",ref($content);
#print: reftype:HASH       ^   
           #therefore the  +------- is a SCALAR value containing a reference to hash

它是一个hashref – 你可以转储所有密钥

print "key: $_n" for keys %{$content}; #or in short %$content
#prints: key: items

你也可以将“items”(arrayref)的值赋给标量变量

my $aref = $content->{items};   #$hashref->{key}
#or
#my $aref = ${$content}{items}; #$hash{key}

但不是

#my $aref = $content{items};    #throws error if "use strict;"
#Global symbol "%content" requires explicit package name at script.pl line 20.

$content {item}正在请求散列％内容中的值,并且您从未定义/分配此类变量. $content是标量变量而不是散列变量％content.

{
    #in perl 5.20 you can also
    use 5.020;
    use experimental 'postderef';
    print "key-postderef: $_n" for keys $content->%*;
}

现在再深入 – 到arrayref – 再次打印出引用类型

printf "reftype:%sn",ref($aref);
#reftype:ARRAY

打印数组的所有元素

print "arr-item: $_n" for @{$aref};

但同样不是

#print "$_n" for @aref;
#dies: Global symbol "@aref" requires explicit package name at script.pl line 37.

{
    #in perl 5.20 you can also
    use 5.020;
    use experimental 'postderef';
    print "aref-postderef: $_n" for $aref->@*;
}

这是一个简单的规则：

my @arr;               #array variable
my $arr_ref = @arr;   #scalar - containing a reference to @arr

@{$arr_ref} is the same as @arr 
 ^^^^^^^^^^ - array reference in curly brackets

如果您有$arrayref – 请在任何地方使用@ {$array_ref}来使用数组.

my %hash;              #hash variable
my $hash_ref = %hash; #scalar - containing a reference to %hash

%{$hash_ref} is the same as %hash
 ^^^^^^^^^^^ - hash reference in curly brackets

如果你有$hash_ref – 在你想要的任何地方使用％{$hash_ref}来使用哈希.

对于整个结构,以下

say $content->{items}->[0];
say $content->{items}[0];
say ${$content}{items}->[0];
say ${$content}{items}[0];
say ${$content->{items}}[0];
say ${${$content}{items}}[0];

打印相同的值1.