In-depth understanding of the count function in PHP, in-depth understanding of the phpcount_PHP tutorial

In-depth understanding of the count function in PHP, in-depth understanding of phpcount

In PHP programming, when traversing an array, it is often necessary to first calculate the length of the array as a condition for determining the end of the loop. Array operations are very frequent in PHP, so count is also a commonly used function. Let’s study the specific implementation of the count function.

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count

int count ( mixed $array_or_countable [, int $mode = COUNT_NORMAL ] )

The count function counts the number of all elements in an array or object.

For objects, if you install the SPL extension, you can call the count function by implementing the Countable interface. The Countable interface has one and only one method, Countable::count(), which returns the return value of the count() function.

Parameter Description

mode

If the parameter mode is set to COUNT_RECURSIVE (or 1), count() will recursively calculate the array. Especially useful when calculating multi-dimensional arrays.

If the first parameter is not an array or an object that implements the Countable interface, the count function will return 1.

Note: The count function can detect recursion to avoid infinite loops, but will return an E_WARNING prompt when encountering infinite recursion or getting a value larger than expected.

Run the example

Normal Application

$arr1 = array(1, 2, 3, 4, 5);
$val1 = count($arr1); // 5

Multidimensional array

$arr2 = array('apple', 'banana', array('cat', 'camel'), 'dog');
$val2_1 = count($arr2); // 4
$val2_2 = count($arr2, 1); // 6

Numbers and strings

$str = "hello world";
$int_val = 1;
$val3 = count($str); // 1
$val4 = count($int_val); // 1

Common objects

class User {
  private $name;
  private $address;
}

$user = new User();
$val5 = count($user); // 1
$val6 = count((array) $user); // 2

array-like object

class User extends ArrayObject {
    private $name;

    public function __construct() {
      $this->name = 'hhq';
    }

    public function getName() {
      return $this->name;
    }

    public function count() {
      return 2;
    }

  }

  $user2 = new User();
  $val7 = count($user2); // 2

Implement Countable interface object

class User implements Countable {
    public function count() {
      return 3;
    }
  }

  $user3 = new User();
  $val8 = count($user3); // 3

Run steps

Enter the switch statement to detect parameter types

If it is NULL, return 0 directly

If it is an array, call the php_count_recursive function to automatically select the number of array elements

If it is an object, first check whether it is an array-like object. If so, calculate the number of array objects

Otherwise, if the object implements the Countable interface, call Countable's count method

Finally, other types such as integer arrays or strings return 1.

Source code interpretation

If it is an ordinary array, the count function will call the php_count_recursive function to implement its function. The running steps are as follows:

If the number of times the current hash bucket is recursively accessed is greater than 1, it means repeated recursion and an E_WARNING error will be returned

Otherwise, calculate the number of array elements of the current array level

If there is a recursive parameter option, continue recursive access

If the parameter is an object type, the implementation will first determine whether the handler is defined. The handler is the structure of the object in the PHP kernel, which contains the count_elements field, which is actually a function. If an object behaves like an array, which is commonly known as an array-like object, then the count_elements function will be executed. The specific implementation is that the class inherits PHP's ArrayObject and implements the count function in the class. The specific call is the count function. If the class does not implement the count function, count returns 0, otherwise the return value of the object's count function is returned.

If it is another data type

1. String

2. Numbers

3. When both if judgments in the object branch are false, that is, the ArrayObject is not inherited and the Countable interface is not implemented.

These types all return 1.

It should be noted that if you need to calculate the number of attributes of an object, you can first convert the object into an array and then call the count function. Such as:

$count_value = count((array) $user);

Summary

While reading the source code of the count function, I got stuck at one step, which is the if (Z_OBJ_HT_P(array)->count_elements) step. Because I still couldn’t write the demo of entering this branch, I searched a lot of information on the Internet. To no avail, I consulted TIPI's reeze and finally got the answer I wanted. If you don’t understand, just ask, haha.