How to copy an array in php? Method introduction

In PHP, array is a very important and commonly used data type. Arrays can store multiple values, and these values ​​can be any type of data. When working with arrays, we sometimes need to copy an element in the array.

For PHP arrays, there are two ways to copy an array, one is to use the assignment operator " = " directly, and the other is to use the array_slice function in PHP. Below we introduce the specific usage of these two methods respectively:

1. Use the assignment operator directly

In PHP, the array is a composite data type, and the value is stored in memory , and variables are just pointers to store values ​​in memory. Therefore, when we assign an array to another variable in PHP, we are actually copying the pointer, that is, the pointer of the original array is copied to the new variable. In this way, you can directly copy the pointer of an element in the original array without copying the actual value of the element. The sample code is as follows:

$arr1 = array('a', 'b', 'c', 'd', 'e');
$arr2 = &$arr1;

In this example, we create an array $arr1 containing 5 elements, and then assign its pointer to a new array $arr2. At this time, if any element in $arr1 is modified, the corresponding element in $arr2 will also be modified. This is because they share the same pointer, pointing to the same memory.

2. Using the array_slice function

Different from using the assignment operator directly, the array_slice function in PHP can copy an element in the original array and return an A new array that is different from the original array. The usage of this function is as follows:

$input = array('a', 'b', 'c', 'd', 'e');
$offset = 2;
$length = 1;
$output = array_slice($input, $offset, $length);

In this example, we create an array $input containing 5 elements, and then use the array_slice function to copy its 3rd element from the original array and store it in In a new array $output. The $offset parameter indicates where to start copying, and the $length parameter indicates how many elements to copy.

It should be noted that using the array_slice function to copy array elements will not affect the elements in the original array. Therefore, if we want to modify the new array without affecting the original array, we should use this method to copy. In addition, when the variable referenced by a pointer in PHP changes, the referenced variable will also change. This requires us to be careful about using reference variables when copying arrays.

Summary

In PHP, copying an array is a common operation. You can use the assignment operator to directly copy the pointer of an element in the original array, or you can use the array_slice function to copy a new array. Both methods are useful in different scenarios. However, it is important to be careful when using reference variables to avoid unexpected errors.

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