How to reference and change an array in php

In PHP, array is a very common and practical data structure. In practical applications, it is often necessary to reference an array and modify it. This article will introduce in detail how PHP references and changes arrays.

1. Introduction to PHP arrays

In PHP, an array is a data structure that can store multiple values. PHP arrays can contain different types of data, such as strings, numbers, objects, etc. PHP array elements can be accessed through subscripts, which can be any type of value such as integers or strings.

There are two types of arrays in PHP: numeric arrays and associative arrays. A numeric array refers to an array whose subscripts are integers. The subscripts start counting from 0 and each element is separated by a comma. An associative array is an array whose subscripts are strings. In each element, the key and value are separated by an equal sign and each element is separated by a comma.

The following is a sample code to create a PHP array:

// 创建数值数组
$numbers = array(1, 2, 3, 4, 5);

// 创建关联数组
$person = array("name" => "John", "age" => 30, "address" => "123 Main Street");

2. PHP array reference

PHP array reference refers to assigning variables to elements of the array and modifying them. When referencing an element in an array, PHP will use the value of the element as a copy of the variable, so if the variable is modified, the value of the corresponding element in the original array will also change.

Here is a sample code to reference a PHP array element:

// 创建数值数组
$numbers = array(1, 2, 3, 4, 5);

// 引用数组元素
$item =& $numbers[2];

// 修改变量值
$item = 10;

// 输出数组元素
echo $numbers[2];  //输出10

In the above example, we referenced the third element of the $numbers array and named it $item. We modify the value of $item to 10, and then output the value of $numbers[2], and the result is 10.

Similarly, we can also reference elements of associative arrays. The following is a sample code that references an associative array element:

// 创建关联数组
$person = array("name" => "John", "age" => 30, "address" => "123 Main Street");

// 引用数组元素
$item =& $person["age"];

// 修改变量值
$item = 40;

// 输出数组元素
echo $person["age"];  //输出40

In the above example, we referenced the "age" element of the $person array and named it $item. We modify the value of $item to 40, and then output the value of $person["age"]. The result is 40.

3. Precautions for PHP array reference

When using reference array elements, there are several things to pay attention to:

1. When referencing numeric array elements, you must Use the & symbol, otherwise a new copy of the element will be made instead of referencing the original element.

2. When referencing an associative array element, the & symbol must be placed in front of the array element, otherwise a new copy of the element will be generated.

3. When the value of the referenced array element is modified, the value of the element in the original array will also change accordingly.

4. Example application of PHP array reference

The following is a custom function and its test code to demonstrate how to use a reference array to change the value of function parameters in PHP.

<?php
//定义自定义函数
function increment(&$numbers) {
    for($i=0; $i<count($numbers); $i++) {
        $numbers[$i]++;
    }
}

//测试函数
$numbers = array(1, 2, 3, 4, 5);
increment($numbers);
print_r($numbers);
?>

In the above code, we have defined a custom function called increment that accepts an array as a parameter and increments the value of each element by referencing the array. We then created the $numbers array of values ​​in our test code and passed it as a parameter when calling the increment function. Finally, we use the print_r function to display the modified value of the $numbers array.

Execute the above code, the output result is as follows:

Array ([0] => 2 [1] => 3 [2] => 4 [3] => 5 [4] => 6)

The above code demonstrates how to use PHP array reference to modify the value of function parameters. Inside the function we iterate over the array elements using a foreach loop and increment its value by reference and then iterate over the array again and output its value using the print_r function.

5. Conclusion

In PHP, using arrays is very common because they can store and process any type of data. By using a reference array, we can modify the value of an array element without creating a new copy. In practical applications, we often need to use reference arrays to implement various algorithms and data structures in computer science without worrying about wasting memory and time. In short, PHP's basic arrays and reference arrays are important concepts and techniques worth mastering.

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