How to get the name of the first key of a specified array in PHP

php editor Xiaoxin will introduce to you how to get the name of the first key of the specified array. In PHP, you can use the array_keys() function to get all keys of an array and get the first key by index. Another method is to use the reset() function to point the internal pointer of the array to the first element and return the corresponding key name. Both methods can easily obtain the name of the first key of the specified array, making your PHP programming more efficient and convenient.

PHP Gets the name of the first key of the specified array

In php, there are many ways to get the name of the first key of the array:

1. Use array_keys() function

array_keys() The function returns an array of all keys in the array. To get the name of the first key you can use:

$arr ​​= array("a" => 1, "b" => 2, "c" => 3);
$first_key = array_keys($arr)[0]; // Output: "a"

2. Use foreach loop

You can use foreach to loop through the elements of the array one by one. The name of the first key will be the first value of the loop:

$arr ​​= array("a" => 1, "b" => 2, "c" => 3);
foreach ($arr as $key => $value) {
$first_key = $key; // Output: "a"
break;
}

3. Use reset() function

reset() The function resets the internal pointer to the first element of the array, and then returns the key name of the element:

$arr ​​= array("a" => 1, "b" => 2, "c" => 3);
$first_key = reset($arr); // Output: "a"

4. Use array_shift() function

array_shift() The function deletes and returns the first element from the array. The key name of the element is the name of the first key:

$arr ​​= array("a" => 1, "b" => 2, "c" => 3);
$first_key = array_shift($arr); // Output: "a"

5. Using the array_first_key() function in PHP 7.3

PHP 7.3 introduced the array_first_key() function, which is specially used to get the first key name of the array:

$arr ​​= array("a" => 1, "b" => 2, "c" => 3);
$first_key = array_first_key($arr); // Output: "a"

Performance comparison

In large arrays, the array_keys() function is more efficient than other methods because it only needs to traverse the array once. For small arrays, all methods are approximately equally efficient.

Notice:

• If the array is empty, the above method will return NULL.
• For associative arrays, the key name can be of any type, including numbers.

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