PHP 函数返回 null 而不是布尔值

Question

在assessageee.com 上的一个PHP 问题中，代码如下：$a = "";echo gettype($a);echo empty($a);echo is_null($a);echo isset($x);仅返回“string1”为什么我们不返回三个布尔值，一个对应三个函数：empty()、is_null() 和 isset()？

Answer 1

echo gettype($a);  // outputs "string"

echo empty($a);    // outputs true, in your environment this is 1

echo is_null($a);  // outputs false, "" isn't null, in your environment this is probably blank

echo isset($x);    // outputs false, in your environment this is probably blank

Answer 2

你得到所有的结果：字符串、真、假和假

echo gettype($a);  // outputs "string"

echo empty($a);    // outputs 1 (true)

echo is_null($a);  // outputs false, or "" in echo

echo isset($x);    // outputs false, or "" in echo

您可以尝试以这种方式运行它以查看不同的结果：

echo gettype($a),'-',empty($a),'-',is_null($a),'-',isset($x),'-';

输出：string-1---

Answer 3

echo gettype($a);  // Outputs a "string" because the datatype used is a string

echo empty($a);    // Outputs true, because the criteria that it is an empty string

echo is_null($a);  // Outputs false, "" isn't null, this is probably blank

echo isset($x);    //Outputs false because isset means "is set"