How to get the key value of an array in php? Brief analysis of methods

In PHP, array is one of the very important data types. When dealing with arrays, we usually need to get the array key values. This article will introduce some methods to obtain array key values.

1. Use the array_keys function

The array_keys function can return a new array containing all the key names of the array. For example:

$arr = array('a' => 1, 'b' => 2, 'c' => 3);
$keys = array_keys($arr);
print_r($keys);

Output result:

Array ( [0] => a [1] => b [2] => c )

As you can see, the $keys array contains all the key names in the $arr array.

If we only want to get the key name of a specific value, we can use the array_search function. It searches the specified value in the array and returns the corresponding key. For example:

$arr = array('a' => 1, 'b' => 2, 'c' => 3);
$key = array_search(2, $arr);
echo $key;

Output result:

b

As you can see, we successfully obtained the key name with value 2 in the $arr array.

2. Use the key function

The key function can return the key name pointed to by the current pointer in the array. It can be combined with a foreach loop to iterate over the key names and key values ​​in the array. For example:

$arr = array('a' => 1, 'b' => 2, 'c' => 3);
foreach ($arr as $key => $value) {
    echo "键名：$key，键值：$value<br>";
}

Output result:

键名：a，键值：1
键名：b，键值：2
键名：c，键值：3

As you can see, we successfully traversed the key names and key values ​​in the $arr array. In the foreach loop, the key function returns the key name pointed to by the current pointer in each loop.

3. Using the array_flip function

The array_flip function swaps the keys and values ​​in an array and returns a new array. For example:

$arr = array('a' => 1, 'b' => 2, 'c' => 3);
$new_arr = array_flip($arr);
print_r($new_arr);

Output result:

Array ( [1] => a [2] => b [3] => c )

You can see that the key name in the $new_arr array is the value in the original array, and the value is the key name in the original array. We can get the key name in the original array by looking up the value in the $new_arr array.

4. Use the array_key_exists function

The array_key_exists function can check whether the specified key name exists in the array. For example:

$arr = array('a' => 1, 'b' => 2, 'c' => 3);
if (array_key_exists('b', $arr)) {
    echo "存在键名 b";
} else {
    echo "不存在键名 b";
}

Output result:

存在键名 b

As you can see, we successfully checked whether there is an element with the key name 'b' in the $arr array.

Summary

Getting array key values ​​is a very common operation in PHP development. This article introduces four PHP methods to obtain array key values, namely using the array_keys function, key function, array_flip function and array_key_exists function. We can choose the appropriate method to obtain the array key value according to different situations.

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