How to determine whether the associative array key value is empty in php

In php, the key value of an associative array can be any type of data, such as strings, numbers, Boolean values, etc. When accessing a key value in the array, if the key exists, the value corresponding to the key is returned; if the key does not exist, null is returned.

So, how to determine whether the key value of an associative array is empty? Here are several methods.

Method 1: Use isset() function

isset() function can detect whether a variable is set and non-null. When the isset() function is applied to an associative array, you can use the subscript to determine whether the key exists in the array. If it exists and the corresponding value is not null, it returns true, otherwise it returns false.

Sample code:

$arr = array('name' => '张三', 'age' => null);
if (isset($arr['name'])) {
    echo '键name存在，值为：' . $arr['name'] . '<br>';
} else {
    echo '键name不存在<br>';
}
if (isset($arr['age'])) {
    echo '键age存在，值为：' . $arr['age'] . '<br>';
} else {
    echo '键age不存在<br>';
}

Output result:

键name存在，值为：张三
键age不存在

As you can see, the isset() function can determine whether the key of an associative array exists, and can determine the corresponding value. Whether it is empty. However, it should be noted that the isset() function can distinguish between the case where the variable value is null and the variable does not exist, but it cannot distinguish between the case when the variable value is false and the variable does not exist.

Method 2: Use the array_key_exists() function

The array_key_exists() function can detect whether a specified key exists in an array. Returns true when the key exists in the associative array; otherwise returns false. Unlike the isset() function, the array_key_exists() function cannot determine whether the corresponding key value is empty.

Sample code:

if (array_key_exists('name', $arr)) {
    echo '键name存在<br>';
} else {
    echo '键name不存在<br>';
}
if (array_key_exists('age', $arr)) {
    echo '键age存在<br>';
} else {
    echo '键age不存在<br>';
}

Output result:

键name存在
键age存在

As you can see, the array_key_exists() function can determine whether the key of an associative array exists, but it cannot determine the corresponding value. Whether it is empty.

Method 3: Use the empty() function

The empty() function can detect whether a variable is empty. When the key exists in the associative array and the corresponding value is not empty, it returns false; otherwise it returns true.

Sample code:

if (empty($arr['name'])) {
    echo '键name为空<br>';
} else {
    echo '键name非空，值为：' . $arr['name'] . '<br>';
}
if (empty($arr['age'])) {
    echo '键age为空<br>';
} else {
    echo '键age非空，值为：' . $arr['age'] . '<br>';
}

Output result:

键name非空，值为：张三
键age为空

As you can see, the empty() function can determine whether the key value of an associative array is empty. However, it should be noted that the empty() function treats values ​​such as 0, '0', false, and ' ' as empty, which may lead to some unexpected results.

In summary, the above three methods can be used to determine whether the key value of an associative array is empty. It is necessary to choose the appropriate method to use according to the specific business scenario.

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