How to determine whether a certain key exists in an array in php

In PHP, sometimes we need to operate on an array, such as determining whether a key exists. When processing an array, it is a very common operation to determine whether a certain key exists in the array. Let's take a look at how to implement this operation.

First, we need to define an array in PHP, and then determine whether a certain key exists in the array. The following is a basic array example:

$arr = array(
  'name' => '张三',
  'age' => 30,
  'address' => '北京市朝阳区',
);

Next, we will introduce two methods to determine whether a certain key exists in the array.

isset() function

In PHP, we can use the isset() function to determine whether the value of a variable or an array exists. Among them, if the key of an array exists and its value is not NULL, the isset() function returns true, otherwise it returns false. In other words, if we want to determine whether a key in an array exists, we can use the following code:

if (isset($arr['name'])) {
  echo '存在name键';
} else {
  echo '不存在name键';
}

In the above code, if $arr exists in the array named 'name' key, then output name key exists, otherwise output name key does not exist.

In addition, you can also check whether multiple keys exist together. For example, we can check whether keys named 'name', 'age', 'address' all exist:

if (isset($arr['name'], $arr['age'], $arr['address'])) {
  echo '这三个键都存在';
} else {
  echo '至少有一个键不存在';
}

array_key_exists () Function

In addition to using the isset() function, we can also use the array_key_exists() function to check whether a certain key exists in an array. The usage is also very simple. The code is as follows:

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

is similar to isset() function. If there is a named 'name'# in the $arr array ## key, then output exists name key , otherwise output does not exist name key .

It should be noted that

array_key_exists() can be used to find multi-dimensional arrays, while isset() does not support this enough. For example:

$arr2 = array(
  'person' => array(
    'name' => '小明',
    'age' => 18
  ),
  'animal' => array(
    'name' => '小狗',
    'age' => 2
  ),
);

if (array_key_exists('person', $arr2) && array_key_exists('name', $arr2['person'])) {
  $person_name = $arr2['person']['name'];
  echo '人的姓名是：' . $person_name;
}

In the above code, we check whether the keys named

'person' and 'name' in the $arr2 array All exist. If they all exist, the output of the person's name is 'Xiao Ming'.

To sum up, we can use the

isset() and array_key_exists() functions to check whether a key exists in the array. Among them, isset() is suitable for simple array searches, while array_key_exists() is more suitable for multi-dimensional array searches. You need to choose which function to use to check whether a certain key exists in the array based on actual needs.

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