perl - perl 中访问散列变量的不同方式有哪些

Question

根据我的基本理解，我们可以按如下方式访问哈希值:

$hash_name{key1}{key2};       #In case of an nested hash 
$hash_reference->{key1}{key2} #if we have the reference to the hash instead of the hash we can access as 

但在其中一个存档代码中，我看到如下:

$sc1 = %par->{'a'}{'b'};
@a1 = %par->{'a'}{'c'};
%c3 = %par->{'a'}{'d'};

它实际上是什么意思？有人可以帮助我吗？

Answer 1

您发布的所有三个变体在 use strict 下都会产生语法错误，以及 use warnings 的附加警告在 Perl 5.22 之前的 Perls 上。我在这里展示的输出来自 Perl 5.20.1。

use strict;
use warnings;

my $par = { a => { b => 1, c => 2, d => 3 } };

my $sc1 = %par->{'a'}{'b'};
my @a1 = %par->{'a'}{'c'};
my %c3 = %par->{'a'}{'d'};

__END__
Using a hash as a reference is deprecated at /home/foo/code/scratch.pl line 700.
Using a hash as a reference is deprecated at /home/foo/code/scratch.pl line 701.
Using a hash as a reference is deprecated at /home/foo/code/scratch.pl line 702.
Global symbol "%par" requires explicit package name at /home/foo/code/scratch.pl line 700.
Global symbol "%par" requires explicit package name at /home/foo/code/scratch.pl line 701.
Global symbol "%par" requires explicit package name at /home/foo/code/scratch.pl line 702.
Execution of /home/foo/code/scratch.pl aborted due to compilation errors.

无 strict和 warnings ，它会编译，但会产生废话。

no strict;
no warnings;
use Data::Printer;

my $par = { a => { b => 1, c => 2, d => 3 } };

my $sc1 = %par->{'a'}{'b'};
my @a1 = %par->{'a'}{'c'};
my %c3 = %par->{'a'}{'d'};

p $sc1;
p @a1;
p %c3;

__END__

undef
[
    [0] undef
]
{
    ''   undef
}

也就是说，总是 use strict和 use warnings对于您的 Perl 程序，并听取它向您显示的警告。