Detailed explanation of the usage of PHP array_keys() function

PHP array_keys() function usage details

array_keys() is a very commonly used array function in PHP. It can be used to obtain all the key names in the array and return an array containing the obtained key names. Below we will explain its usage in detail.

1. Function description

array_keys($array, $search_value, $strict);

Parameter description:

$array: Required parameter, input array.

$search_value: Optional parameter, value used to search.

$strict: Optional parameter, perform identical comparison. The default is false, which uses relaxed comparison.

Return value:

If $search_value is not set, all key values ​​in $array are returned.

If $search_value is set, return the key value matching $search_value in $array.

2. Usage Example

The following is a simple example showing how to use the array_keys() function to get the key names in an array:

<?php
  $array = array('a' => 'apple', 'b' => 'banana', 'c' => 'cherry', 'd' => 'durian');

  // 获取数组中所有的键名
  $keys = array_keys($array);
  print_r($keys);

  // 获取数组中的键名，搜索值为'banana'
  $banana_keys = array_keys($array, 'banana');
  print_r($banana_keys);
?>

Output The results are as follows:

Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
)
Array
(
    [0] => b
)

3. Advanced usage

3.1 Return the key name of the first matching item

If $search_value is not found in the specified array, array_keys() will return an empty array. However, we can use the array_slice() function and the current array pointer to get the first key name.

The following example shows how to get the key name of the first matching entry:

<?php
  $array = array('a' => 'apple', 'b' => 'banana', 'c' => 'cherry', 'd' => 'durian', 'e' => 'banana');

  // 获取数组中的键名，搜索值为'banana'
  $banana_keys = array_keys($array, 'banana');

  if (count($banana_keys) > 0) {
      $first_banana_key = current(array_slice($banana_keys, 0, 1));
      echo '第一个匹配项的键名：' . $first_banana_key;
  }
?>

The output is as follows:

第一个匹配项的键名：b

3.2 Using strict comparison

We can Use the third parameter $strict to enable equality comparison. It will ensure that the values ​​are of the same data type before matching.

The following example illustrates how to use $strict to perform a congruent comparison:

<?php
  $array = array('1' => 'apple', '2' => 'banana', '3' => 'cherry');
  
  // 未使用严格比较，输出结果为 '2'
  $keys = array_keys($array, '2');
  echo '未使用严格比较：';
  print_r($keys);

  // 使用严格比较，输出结果为空数组
  $keys = array_keys($array, '2', true);
  echo '使用严格比较：';
  print_r($keys);
?>

The output is as follows:

未使用严格比较：Array ( [0] => 2 )
使用严格比较：Array ( )

4. Summary

array_keys() is a very convenient array function in PHP, which can be used to get all the key names in the array. We can use optional parameters to search for a specific value and use the third parameter to enable strict comparison.

Although array_keys() is very powerful, we should still be careful when dealing with large arrays. If used carelessly it can either cause out of memory or consume a lot of time. Therefore, performance and scalability issues should be considered when writing code.

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