PHP readdir() 并返回一个虚假值

Question

根据 https://www.php.net/manual/en/function.readdir.php 上的信息，readdir() 函数

may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE.

因此建议使用 === 进行测试。

这可能是什么非布尔值？在我的测试中，我只能得到一个错误的 false，就像下面的例子：

$dirname='0';   //  misinterpreted
print $dirname==false?'false':'true';

所有其他字符串都被解释为 true。

是否有任何其他字符串的计算结果为 false？或者是否有其他 return 结果会被评估为 false？

Answer 1

Are there any other strings which would evaluate to false? Or is there some other return result which would evaluate as false?

布尔类型的手册列出了所有被视为假的值，https://www.php.net/manual/en/language.types.boolean.php#language.types.boolean.casting:

When converting to boolean, the following values are considered FALSE:

the boolean FALSE itself

the integers 0 and -0 (zero)

the floats 0.0 and -0.0 (zero)

the empty string, and the string "0"

an array with zero elements

the special type NULL (including unset variables)

SimpleXML objects created from empty tags

和readdir

[r]eturns the entry name on success or FALSE on failure

- 所以除非你得到假，否则该值应该始终是一个字符串。（目录条目始终被视为字符串值，在该级别上不存在“数字”的概念。）

PHP readdir() 并返回一个虚假值

PHP readdir() and returning a falsy value

php

boolean

readdir