A brief discussion on PHP source code 4: About the count function

This article mainly introduces a brief discussion on PHP source code four: Regarding the count function, it has a certain reference value. Now I share it with you. Friends in need can refer to it

In some interviews or exams We often see the count function, so we took a closer look

For count processing of non-arrays
You can see it in its code

PHP_FUNCTION(count){
    zval *array;
    long mode = COUNT_NORMAL;
    if (zend_parse_parameters (ZEND_NUM_ARGS() TSRMLS_CC, "z|l", &array, &mode) == FAILURE)
        return;
    switch (Z_TYPE_P(array)) {
        case IS_NULL:    //    空值处理
            RETURN_LONG(0);
            break;
        case IS_ARRAY:    //    处理数组，包括其是递归
            RETURN_LONG (php_count_recursive (array, mode TSRMLS_CC));
            break;
        case IS_OBJECT: {    
    #ifdef HAVE_SPL
        /* it the object implements Countable we call its count() method */
            zval *retval;             if (Z_OBJ_HT_P(array)->get_class_entry && instanceof_function(Z_OBJCE_P(array), spl_ce_Countable TSRMLS_CC)) {
                zend_call_method_with_0_params(&array, NULL, NULL, "count", &retval);
                if (retval) {
                    convert_to_long_ex(&retval);
                    RETVAL_LONG(Z_LVAL_P(retval));
                    zval_ptr_dtor(&retval);
                }
            return;
            }
    #endif
        /* if not we return the number of properties (not taking visibility into account) */
            if (Z_OBJ_HT_P(array)->count_elements) {
                RETVAL_LONG(1);
                if (SUCCESS == Z_OBJ_HT(*array)->count_elements(array, &Z_LVAL_P(return_value) TSRMLS_CC)) {
                    return;    
              }
            }
        }
    default:    //    其它情况，如考试中常见的字符串等
        RETURN_LONG(1);
        break;
    }}

It is explained in the manual:

For objects, if SPL is installed, this function can call count() by implementing the Countable interface. This interface has only one method, count(), which returns the return value of the count() function.

For the statistics of array length, if mode uses the default value (0), only the length of the first dimension array will be displayed
The code is as follows

 $arr = array(1, 2, 3);
 $arr2 = array($arr, $arr);
 echo count($arr2), &#39;<br />&#39;;
 echo count($arr2, 1);
 /*   输出结果：28*/

If only the first dimension is displayed Array, then directly return the nNumOfElements attribute of the HashTable that saves the array.
The implementation code is:

  //    php_count_recursive函数 array.c 251行cnt = zend_hash_num_elements(Z_ARRVAL_P(array)); 
ZEND_API int zend_hash_num_elements(HashTable *ht){
    IS_CONSISTENT(ht);     return ht->nNumOfElements;}

If you want to directly run some simple operations of HashTable, click on the simple example of HashTable in the PHP source code
If you want to see how arrays are stored or traversed, click on Brother Bird's in-depth understanding of PHP arrays (traversal order)

If recursion is started, use count($arr, 1)
The program will recursively call the php_count_recursive function
For HashTable, the program will traverse the doubly linked list containing this dimensional array, and then recursively traverse the pData stored in each node until all nodes are traversed

[Feeling]
HashTable is very powerful. If you want to calculate the length of an array or call the count function, reinventing the wheel will be a thankless task!

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