＆是什么QUOT; 0，但真正的＆QUOT;在Perl意味着什么呢？ [英] What does "0 but true" mean in Perl?

问题描述

有人能解释究竟是什么字符串0，但真正的是指在Perl？据我了解，它的整数比较等于零，但作为一个布尔值使用时，计算结果为真。它是否正确？这是语言的正常行为或者这是作为跨preTER一个特例？

Can someone explain what exactly the string "0 but true" means in Perl? As far as I understand, it equals zero in an integer comparison, but evaluates to true when used as a boolean. Is this correct? Is this a normal behavior of the language or is this a special string treated as a special case in the interpreter?

推荐答案

这是语言的正常行为。引述 perlsyn 手册页：

It's normal behaviour of the language. Quoting the perlsyn manpage:

数字0，字符串'0'和''，空列表（）和民主基金
  在布尔上下文全是假的。所有其他值都是如此。否定
  一个真正的价值！或者不是返回一个特殊的假值。
  时，因为它被视为''的字符串进行评价，但是作为一个数字，它是
  视为0。

The number 0, the strings ’0’ and ’’, the empty list "()", and "undef" are all false in a boolean context. All other values are true. Negation of a true value by "!" or "not" returns a special false value. When evaluated as a string it is treated as ’’, but as a number, it is treated as 0.

由于这一点，需要有从系统调用需要返回0作为一个（成功）的返回值返回0，并留下了一种信号通过实际返回一个假值故障状态下的一种方式。 0，但真正的供应这一目的。

Because of this, there needs to be a way to return 0 from a system call that expects to return 0 as a (successful) return value, and leave a way to signal a failure case by actually returning a false value. "0 but true" serves that purpose.

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