遍历hash出错

qfmeal

代码如下：
sub func()
{
        my %hash =
        (
                aaa => 111,
                bbb => 222,
                ccc => 333
        );
       
        return \%hash;
}


my $ref_hash = func();

foreach ( my ($key,$value) = each %{$ref_hash} )
{
        print $key," => ",$value,"\n";
}


结果是：
bbb => 222
bbb => 222

我预想的结果应该是：
aaa => 111
bbb => 222
ccc => 333

[ 本帖最后由 qfmeal 于 2009-5-21 17:36 编辑 ]

MMMIX

$enter 是啥？

qfmeal

$enter 是多余的。

yashiro_lj

把foreach改成while即可

参见each函数的说明：
When called in list context, returns a 2-element list consisting of the key and value for the next element of a hash, so that you can iterate over it.
each函数只是返回一个键值对，而不是所有的键值对

[ 本帖最后由 yashiro_lj 于 2009-5-21 17:47 编辑 ]

churchmice

each返回hash的第一个键值对
所以

1. 
   
2. foreach(my($key,$value)=(bbb,222))
   

复制代码

这个循环执行了两次，因为列表有两个元素($key,$value)

你可以打印一下$_看看

1. 
   
2. sub func()
   
3. {
   
4.         my %hash =
   
5.         (
   
6.                 aaa => 111,
   
7.                 bbb => 222,
   
8.                 ccc => 333
   
9.         );
   
10.       
    
11.         return \%hash;
    
12. }
    
13. 
    
14. 
    
15. my $ref_hash = func();
    
16. 
    
17. foreach ( my ($key,$value) = each %{$ref_hash} )
    
18. {
    
19.                                 print $_,"\n";
    
20.         print $key," => ",$value,"\n";
    
21. }
    
22. 
    

复制代码

[ 本帖最后由 churchmice 于 2009-5-21 17:45 编辑 ]

MMMIX

原帖由 churchmice 于 2009-5-21 17:43 发表
each返回hash的第一个键值对

对 hash 来说不存在第几的问题。

qfmeal

改成while就好了。

另外我原想each %hash是返回一个键字/数值对的。

Perl_Er

Traversing a Hash

#-----------------------------
while(($key, $value) = each(%HASH)) {
    # do something with $key and $value
}
#-----------------------------
foreach $key (keys %HASH) {
    $value = $HASH{$key};
    # do something with $key and $value
}
#-----------------------------
# %food_color per the introduction
while(($food, $color) = each(%food_color)) {
    print "$food is $color.\n";
}
# Banana is yellow.
#
# Apple is red.
#
# Carrot is orange.
#
# Lemon is yellow.

foreach $food (keys %food_color) {
    my $color = $food_color{$food};
    print "$food is $color.\n";
}
# Banana is yellow.
#
# Apple is red.
#
# Carrot is orange.
#
# Lemon is yellow.
#-----------------------------
print

"$food

is

$food_color{$food}.\n"

#-----------------------------
foreach $food (sort keys %food_color) {
    print "$food is $food_color{$food}.\n";
}
# Apple is red.
#
# Banana is yellow.
#
# Carrot is orange.
#
# Lemon is yellow.
#-----------------------------
while ( ($k,$v) = each %food_color ) {
    print "Processing $k\n";
    keys %food_color;               # goes back to the start of %food_color
}
#-----------------------------
# download the following standalone program
#!/usr/bin/perl
# countfrom - count number of messages from each sender

$filename = $ARGV[0] || "-";

open(FILE, "<$filename")         or die "Can't open $filename : $!";

while(<FILE>) {
    if (/^From: (.*)/) { $from{$1}++ }
}

foreach $person (sort keys %from) {   
    print "$person: $from{$person}\n";
}

#-----------------------------