How to operate arrays in php? Brief analysis of methods

In PHP, array is a very important data structure that can be used to store multiple values. These values ​​can be of any type, such as numeric values, strings, objects, functions, etc. In PHP, an array is a flexible data type that can be manipulated and processed using various methods. This article will introduce in detail the internal implementation mechanism of PHP arrays, including the underlying data structure and the implementation of array operations.

1. Data structure of array

In PHP, arrays are implemented based on Hash Table. A hash table is a very flexible data structure that can be used to quickly find and access data. Hash tables are usually implemented by storing data in an array, and then mapping each data element to a position in the array through a hash function. A hash function can be any function that can map elements to integers. Common hash functions include modulo operation, multiplicative hashing, MD5, etc.

In PHP, arrays are also implemented based on hash tables. The underlying data structure of the PHP array is a structure array called Bucket. Each Bucket contains three attributes: key, value and next. Among them, key represents the key name of the element, value represents the value of the element, and next represents the position of the next element in the same hash bucket. Because the elements in PHP arrays can be of any type, key and value are represented by zval structures.

2. Array operations

PHP array supports a variety of operations, including adding elements, deleting elements, modifying elements, querying elements, etc. Below we will introduce some of the internal operations of PHP arrays.

2.1 Adding elements

When adding an element to an array, PHP will first calculate its hash value based on the key name of the element. Then the bucket corresponding to the hash value is searched in the Bucket array. If there is already an element in the current bucket, the next empty bucket (that is, the bucket with next = 0) is found through the next attribute, and the new element is added to the bucket. in the barrel. If the current bucket is empty, add the new element to the current bucket.

If the same key name already exists in the array, the new value will overwrite the original value.

2.2 Delete elements

When deleting an element from an array, PHP will first calculate its hash value based on the key name of the element and find the bucket corresponding to the hash value. Then it will traverse the elements in the bucket, find the element with matching key name, and delete the element from the bucket (by assigning the next pointer of the corresponding element in the bucket to the position of the next element, thereby skipping the element).

2.3 Modify elements

When modifying elements in the array, PHP will calculate its hash value based on the key name of the element and find the bucket corresponding to the hash value. Then it will traverse the elements in the bucket, find the element whose key name matches, and modify the value of the element to the new value.

2.4 Query elements

When querying elements in an array, PHP will calculate its hash value based on the key name of the element and find the bucket corresponding to the hash value. Then it will traverse the elements in the bucket, find the element whose key name matches, and return the value of the element.

3. Performance considerations

Since PHP arrays are implemented based on hash tables, the time complexity of accessing elements in the array is O(1). However, if there are a lot of conflicts in the array, that is, if multiple elements are mapped to the same bucket, accessing elements will be less efficient. In order to avoid this situation, PHP implements a mechanism called Load Factor in the hash table. When the number of elements in the array reaches a certain threshold, PHP will reallocate a larger bucket array, recalculate the hash value of the original elements and add them to the new bucket.

In addition, PHP also provides a series of optimization methods to improve the performance of arrays, such as different hash functions, comparison functions, etc.

4. Summary

PHP array, as a core data type, is a knowledge point that PHP developers must master. This article introduces in detail the implementation mechanism of PHP arrays, including the underlying hash table library structure and the implementation of array operations. For PHP developers, understanding these details can help us better understand how PHP arrays work, and thus better program PHP.

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