The difference between PHP isset and array_key_exists

The difference between PHP isset and array_key_exists_PHP tutorial

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Release： 2016-07-13 17:14:52

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When determining whether the index value of a certain PHP array exists, isset and array_key_exists are generally used. However, the values returned by the two will be different. Let me introduce the difference between isset and array_key_exists. Friends in need can refer to it. .

Let’s look at a simple example first

The code is as follows

代码如下	复制代码
isset($a['key']) array_key_exists('key', $a)array_key_exists

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isset($a['key'])

array_key_exists('key', $a)array_key_exists

Tells you exactly whether a certain key exists in the array, while isset just returns the status of whether the key value is null.

isset function is to detect whether the variable is set.

Format: bool isset ( mixed var [, mixed var [, ...]] )

Return value:

代码如下	复制代码
$a = array('key1' => '123', 'key2' => null);

1. If the variable does not exist, return FALSE

2. If the variable exists and its value is NULL, it also returns FALSE

3. If the variable exists and the value is not NULL, return TURE

代码如下

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isset($a['key1']); // true
array_key_exists('key1', $a); // true

isset($a['key2']); // false
array_key_exists('key2', $a); // true

4. When checking multiple variables at the same time, TRUE will be returned only when each single item meets the previous requirement, otherwise the result will be FALSE

代码如下

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$a = array ('test' => 1, 'hello' => NULL);

var_dump( isset ($a['test') ); // TRUE
var_dump( isset ($a['foo') ); // FALSE
var_dump( isset ($a['hello') ); // FALSE

// 'hello' 等于 NULL，所以被认为是未赋值的。
// 如果想检测 NULL 键值，可以试试下边的方法。
var_dump( array_key_exists('hello', $a) ); // TRUE

Example 1

The code is as follows

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$a = array('key1' => '123', 'key2' => null);