在 Perl 中，值可以未初始化但仍已定义吗？
在 win32 上运行 ActiveState Perl 5.10.1。
这段代码是怎么回事：
die(defined($r->unparsed_uri =~ '/(logout.pl)?$'));
...dies with 1，而将同一行更改为：
die($r->unparsed_uri =~ '/(logout.pl)?$');
...dies with Use of uninitialized value in die？
它是如何已定义但未初始化的？我认为未初始化意味着未定义。
Running ActiveState Perl 5.10.1 on win32.
How is it that this code:
die(defined($r->unparsed_uri =~ '/(logout.pl)?
...dies with 1, whereas changing the same line to say this:
die($r->unparsed_uri =~ '/(logout.pl)?
...dies with Use of uninitialized value in die?
How is it defined yet uninitialized? I thought uninitialized meant undefined.
));
...dies with 1, whereas changing the same line to say this:
...dies with Use of uninitialized value in die?
How is it defined yet uninitialized? I thought uninitialized meant undefined.
);
...dies with Use of uninitialized value in die?
How is it defined yet uninitialized? I thought uninitialized meant undefined.
...dies with 1, whereas changing the same line to say this:
...dies with Use of uninitialized value in die?
How is it defined yet uninitialized? I thought uninitialized meant undefined.
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（2）
在第一种情况下，匹配操作发生在标量上下文中。在第二种情况下，它发生在数组上下文中，几乎就像您编写的那样：
如果
$r->unparsed_uri匹配模式，但$1未定义，因为匹配的字符串以“/”结尾，那么@groups将是一个长度为1的数组，包含单个元素undef。把它们放在一起，就好像你在说：
In the first case, the matching operation is taking place in scalar context. In the second case, it's taking place in array context, almost as if you had written:
If
$r->unparsed_urimatches the pattern, but$1is undefined because the matched string ended with "/", then @groups will be an array of length 1, containing the single elementundef.Put it all together, it's as if you'd said:
您启用了警告吗？
鉴于
我明白
这解释了发生了什么。
$uri未定义，因此您会在m//中使用它时收到警告。由于$uri未定义，因此匹配结果为false，但已定义。因此，define返回 true，die输出1。Do you have warnings enabled?
Given
I get
which explains what is going on.
$uriis not defined, so you get a warning for using that inm//. Because$uriis not defined, the result of the match is false but defined. Hence,definedreturns true anddieoutputs1.