我有一系列哈希：
my @questions = (
{"Why do you study here?" => "bla"},{"What are your hobbies?" => "blabla"});
我尝试循环它：
foreach (@questions) {
my $key = (keys $_)[0];
$content .= "\\section{$key}\n\n$_{$key}\n\n";
}
给我
Use of uninitialized value in concatenation (.) or string at
convert.pl line 44.
错误来自哪里？
解决方法
Gilles already explained如何使用您当前的数据结构,但我建议您完全使用不同的数据结构：简单的哈希.
#!/usr/bin/perl
use strict;
use warnings;
use 5.010;
my %answers = (
"Why do you study here?" => "bla","What are your hobbies?" => "blabla"
);
while (my ($question,$answer) = each %answers) {
say "Question: $question";
say "Answer: $answer";
}
输出：
Question: Why do you study here? Answer: bla Question: What are your hobbies? Answer: blabla
我发现这比哈希数组更容易使用,每个哈希只包含一个键/值对.
如果您想以某个(非排序)顺序遍历哈希,则有几个选项.简单的解决方案是按照您要访问它们的顺序维护一组键：
# In the order you want to access them
my @questions = ("What are your hobbies?","Why do you study here?");
my %answers;
@answers{@questions} = ("blabla","bla");
foreach my $question (@questions) {
say "Question: $question";
say "Answer: $answers{$question}";
}
输出：
Question: What are your hobbies? Answer: blabla Question: Why do you study here? Answer: bla
另一种选择是使用Tie::IxHash(或更快的XS模块Tie::Hash::Indexed)按插入顺序访问密钥：
use Tie::IxHash;
tie my %answers,"Tie::IxHash";
%answers = (
"Why do you study here?" => "bla",$answer) = each %answers) {
say "Question: $question";
say "Answer: $answer";
}
输出：
Question: Why do you study here? Answer: bla Question: What are your hobbies? Answer: blabla