How to use array_keys function in PHP to get all key names in an array

In PHP, the array_keys function is a function used to obtain all key names in an array. Use it to easily get all the key names in the array and return them into a new array.

The syntax of the array_keys function is as follows:

array array_keys ( array $array [, mixed $search_value = null [, bool $strict = false ]] )

Among them:

• $array represents the array of key names to be obtained.
• $search_value is an optional parameter. If this parameter is passed in, only the key names containing the specified value will be returned, otherwise all key names will be returned.
• $strict is also an optional parameter. If set to true, a strict comparison will be used to compare key names and searched values ​​for equality.

For example, suppose we have an associative array whose key names are "name", "email" and "phone". We can use the array_keys function to get them:

$array = array("name" => "张三", "email" => "zhangsan@example.com", "phone" => "123456789");

$keys = array_keys($array);

print_r($keys); // 输出：Array ( [0] => name [1] => email [2] => phone )

In this example, the $keys variable is a new array containing all the key names in the $array array.

Of course, if we only want to get the key name containing the specified value, we can also pass in the second parameter, as shown below:

// 获取值为"张三"的键名
$keys = array_keys($array, "张三");

print_r($keys); // 输出：Array ( [0] => name )

In this example, we only get the array The median value is the key name of "Zhang San".

It should be noted that if there are multiple elements with the value $search_value in the array, the key names of all these elements will be returned.

Finally, if we want to use strict comparison to determine whether the key name and $search_value are equal, we can set the third parameter to true. For example:

// 不使用严格比较
$keys = array_keys($array, 123456789); // 返回一个空数组

// 使用严格比较
$keys = array_keys($array, 123456789, true); // 输出：Array ( [0] => phone )

In this example, since the string "123456789" and the key name "phone" are not strictly equal, if strict comparison is not used, an empty array will be returned. And if strict comparison is used, only the key name "phone" will be returned.

In general, the array_keys function is a very practical function that can help us easily obtain all the key names in an array and filter and filter as needed.

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