Implemented at the bottom of php array

PHP array is the most important data type in the language, and it plays a very important role in the programming process. PHP's arrays can implement various types of arrays such as one-dimensional arrays, multi-dimensional arrays, and associative arrays in user space. The underlying implementation of PHP arrays uses the hash table algorithm. This article will deeply explore the principles of the underlying implementation of PHP arrays.

Hash table algorithm

The hash table is a data structure used to implement associative arrays. Its core idea is to use keywords as indexes of the array, and use the hash function to convert the keywords into mapped to a position in the array. The main function of the hash function is to map an input (key) of any length to a fixed-length output (hash value), and has good hashing properties, that is, for different inputs, the probability of the resulting hash value colliding is very Small. Each element in the hash table exists in the form of a key-value pair, where the key is the output of the hash function and the value is the corresponding data.

The advantage of hash tables is that they can achieve fast search, insertion and deletion without being affected by the size of the data. However, the disadvantage of the hash table is also obvious, that is, it takes up a large amount of memory space, because the length of the hash table must be larger than the number of key-value pairs to be stored, so as to ensure that the hash function can avoid hashing as much as possible. conflict. At the same time, when the number of keys stored in the hash table is small, the hashing performance of the hash function is not as good as when the number of keys is large.

Implementation principle of PHP array

PHP array is implemented using hash table algorithm. In PHP, arrays can be indexed using either numbers or strings (i.e., associative arrays). When using numeric indexing, these numbers are converted into hash array keys. When using string indexes, they are used directly as keys.

In PHP, the underlying implementation of an array is as an array of "buckets", and each "bucket" corresponds to a hash value. Each bucket is a linked list, which contains all key-value pairs with the same hash value. This bucket-linked list structure can avoid hash collisions well and provide fast insertion and access operations. When an array element is accessed, PHP uses the key's hash value to figure out the key's position in the bucket array and traverses the linked list at that position until it finds the desired element.

In addition to the hash table algorithm, the underlying implementation of PHP arrays also uses some optimization measures to improve its performance. One of the most significant optimization measures is the use of some special hash functions to quickly calculate hash values. At the same time, PHP's arrays also use some memory pool technologies to optimize memory allocation to reduce memory fragmentation and the number of calls to the operating system.

Summary

PHP’s array is one of the important data types in the language, and its underlying implementation uses a hash table algorithm. Since hash tables have the advantages of fast search, insertion, and deletion, PHP arrays can process data more quickly and efficiently in the storage and processing of large-scale data. At the same time, PHP arrays also adopt a series of optimization measures to improve their performance and make them better meet the needs of practical applications.

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