Detailed introduction to the usage of array_walk() function in PHP function library

Detailed introduction to the usage of the array_walk() function in the PHP function library

The array_walk() function is a very commonly used array function in PHP. Its function is to execute user definitions for each element in the array. The function. The use of the array_walk() function can greatly simplify code writing and improve program efficiency, especially when processing arrays. It is very useful.

Usage method

The syntax of the array_walk() function is as follows:
array_walk (array &$array , callable $callback [, mixed $userdata = NULL ] )

Parameter description:

1. $array: required, the array that needs to be processed.
2. $callback: Required, function to be executed.
3. $userdata: Optional, additional parameters passed to the callback function, which can be a value or an array.

Callback function

The callback function is the most important part of array_walk(), it needs to be defined by yourself. The basic syntax of the callback function is as follows:
function callback_function (&$array_item, $array_key, $userdata) {
//function code here
}

where:

1. &$array_item: Required, the value of the current array element. Since functions are passed by reference, elements can be operated directly using the & symbol.
2. $array_key: Optional, the key of the current array element. If you want to operate on the array key, you can use this parameter.
3. $userdata: Optional, additional parameters passed to the callback function, which can be a value or an array.

Example

Let’s look at a simple usage example:

$arr ​​= array(1,2,3,4,5,6,7 );
function multiply(&$item, $key, $factor) {
$item *= $factor;
}
array_walk($arr, 'multiply', 3);
print_r($arr);

The output result is as follows:

Array
(
[0] => 3
[1] => 6
[2] => 9
[3] => 12
[4] => 15
[5] => 18
[6] => 21
)

In the above example, we first define an array $arr, and then define a callback function multiply(). This callback function receives three parameters. The first parameter is the value of the current array element, the second parameter is the key value of the current array element, and the third parameter is the additional parameter passed to the callback function, that is, the multiplier.

In the array_walk() function, we call the array $arr as the first parameter, multiply() as the second parameter, and pass the number 3 as the third parameter to the multiply() function. . In this way, the multiply() function multiplies each element in the array by 3 and directly modifies the array value, ultimately resulting in a new array.

Notes

1. The callback function must have one parameter, which is the value of the current array element. If you need to operate the current key value, you need to add a second parameter.
2. For non-reference arrays, their values ​​cannot be modified directly in the callback function.
3. The key values ​​of the array elements in the callback function are consistent with the original array. Even when array_walk() is used to process an array with non-numeric keys, the key values ​​of the array are still retained.

Summary

The array_walk() function is a very powerful array function that can help us simplify and enhance array processing. In actual development, we can define callback functions according to our own needs and flexibly use the array_walk() function to make the code more concise and efficient.

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