PHP array source code implementation

Arrays in PHP are a very important data type that can be used to store large amounts of data and perform related operations. This article will introduce the source code implementation of PHP arrays.

In PHP, arrays are implemented by the HashTable structure. HashTable is a hash table in PHP, which is implemented based on the open address method. A hash table is a data structure that maps data into memory. It can support operations such as insertion, deletion, and search, and is highly efficient.

In the PHP source code, the definition of HashTable is as follows:

struct _hashtable {
    uint32_t     nTableSize;          // 散列表大小
    uint32_t     nTableMask;          // 散列表大小的掩码，用于取模运算
    uint32_t     nNumOfElements;      // 数据元素的数量
    uint32_t     nNextFreeElement;    // 下一个空闲的索引位置
    Bucket       *arData;             // 存放桶元素的数组
    uint32_t     *pInternalPointer;   // 内部指针
    uint32_t     nInternalPointer;    // 内部指针指向的索引位置
    zend_bool    nApplyCount;         // 应用计数
    zend_bool    bApplyProtection;    // 应用保护标记
    zend_bool    bInconsistent;       // 不一致标记
    dtor_func_t  pDestructor;         // 析构函数指针
};

In HashTable, each element will be stored in a structure called Bucket. The Bucket structure is defined as follows:

typedef struct _bucket {
    zval              val;           // 存储值的zval结构体
    zend_ulong        h;             // 存储哈希表的哈希值
    zend_string      *key;           // 存储键值的字符串
    uint32_t          next;          // 存储下一个元素的索引位置
} Bucket;

As can be seen from the above code, each bucket element has a hash value h, a key value key and a value val. The hash value is calculated by the hash function inside the HashTable. In the hash table, find the corresponding bucket element through the hash value and obtain its corresponding value.

When you need to insert an element into the HashTable, you need to first calculate the hash value of the element and find the corresponding bucket element based on the hash value. If the bucket element is empty, insert the new value into the bucket element; if the bucket element already has an element, you need to find the next empty bucket element and insert the new value into the bucket element. If the HashTable is full, the size of the HashTable needs to be expanded.

When you need to delete an element from the HashTable, you need to first find the bucket element corresponding to the element and delete its corresponding value. If the bucket element is empty, it means that the element does not exist in the HashTable.

When you need to query the elements in the HashTable, you also need to find the corresponding bucket element through the hash value and obtain its corresponding value.

In PHP, arrays not only support numeric indexing, but also string indexing. Therefore, PHP uses a special hash table called a "symbol table" to search for string key values. The implementation method of the symbol table is similar to that of the hash table. The difference is that the hash value needs to be converted into a string and then searched.

In addition to ordinary arrays, PHP also supports associative arrays. An associative array is an array structure whose keys and values ​​are both strings. The implementation of associative arrays is similar to ordinary arrays, only the keys and values ​​need to be stored in Buckets.

In summary, the implementation of PHP arrays mainly relies on hash tables, which use hash functions to map key values ​​to corresponding bucket elements and store the corresponding values. In this way, PHP can quickly perform operations such as inserting, deleting, and searching arrays to meet the needs for efficient data processing in PHP programs.

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