哈希鍵值在perl中的子程序後更改爲數組引用

Question

我在同一個哈希的子程序外部和內部創建鍵。但是，在子例程之後，調用子例程之前創建的鍵中的值現在被解釋爲數組引用。

#!/usr/bin/perl 
use module; 
use strict; 
use warnings; 
my %hash; 
my $count = 0; 

my @array = ("a", "b", "c", "d"); 

for my $letter (@array) { 
    $hash{$letter} = $count; 
    $count++; 
} 

# need "\" to pass in hash otherwise changes 
# will get lost outside of subroutine 
foreach my $x (sort keys %hash) { 
    print "first $hash{$x}\n"; 
} 

module::add_ten(\%hash); 

foreach my $p (sort keys %hash) { 
    # $hash{$p} is printing array references, but before it was 
    # printing the value I desired. What did the subroutine do? 
    print "second $hash{$p} $hash{$p}->{ten}\n"; 
} 

，這裏是與子程序

package module; 

sub add_ten { 
my $count = 10; 
    # this passes the full array as reference 
    my ($hash_ref) = @_; # $hash_ref is actually %hash (yes, the % is not a typo) 
    my @keys = keys $hash_ref; 
    foreach my $ltr (sort keys $hash_ref) { 
     $hash_ref->{$ltr} = { ten => $count }; 
     $count++; 
    } 
} 
1; 

這裏的模塊輸出：

first 0 
first 1 
first 2 
first 3 
second HASH(0x7ff0c3049c50) 10 
second HASH(0x7ff0c3049bc0) 11 
second HASH(0x7ff0c3049b90) 12 
second HASH(0x7ff0c3049b60) 13 

我期待的輸出爲：

first 0 
first 1 
first 2 
first 3 
second 0 10 
second 1 11 
second 2 12 
second 3 13 

我修改了我的模塊：

package module; 

sub add_ten { 
    my $count = 10; 
    # this passes the full array as reference 
    my ($hash_ref) = @_; # $hash_ref is actually %hash (yes, the % is not a typo) 
    my @keys = keys $hash_ref; 
    foreach my $ltr (sort keys $hash_ref) { 
     $hash_ref->{$ltr}{ten}=$count; 
     $count++; 
    } 
} 
1; 

和主腳本（註釋掉使用嚴格，以得到它的工作需要）：

#!/usr/bin/perl 
use module; 
#use strict; 
use warnings; 
my %hash; 
my $count = 0; 

my @array = ("a", "b", "c", "d"); 

for my $letter (@array) { 
    $hash{$letter} = $count; 
    $count++; 
} 

# need "\" to pass in hash otherwise changes 
# will get lost outside of subroutine 
foreach my $x (sort keys %hash) { 
    print "first $hash{$x}\n"; 
} 

module::add_ten(\%hash); 

foreach my $p (sort keys %hash) { 
    print "second $hash{$p} $hash{$p}{ten}\n"; 
} 

，但是這是我試圖去。

Answer 1

$hash_ref是%hash參考，所以，當你改變哈希通過$hash_ref引用的元素的值，你就改變了哈希%hash的值。

這意味着，當你做

$hash_ref->{$ltr} = { ten => $count }; 

你正在做

$hash{a} = { ten => 10 }; 

它應該是毫不奇怪，$hash{a}不再包含零。你將不得不改變你的數據結構。您可以使用下列內容：

$hash{a}{value} = 0; 
$hash{a}{subhash}{ten} = 10;