[PHP source code reading] count function, php source code count function

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. , and 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 <span>count</span> ( <span>mixed</span> <span>$array_or_countable</span> [, int <span>$mode</span> = 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

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

Multidimensional array

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

Numbers and Strings

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

Common objects

<span>class</span><span> User {
    </span><span>private</span> <span>$name</span><span>;
    </span><span>private</span> <span>$address</span><span>;
}

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

array-like object

    <span>class</span> User <span>extends</span><span> ArrayObject {
        </span><span>private</span> <span>$name</span><span>;

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

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

        </span><span>public</span> <span>function</span> <span>count</span><span>() {
            </span><span>return</span> 2<span>;
        }

    }

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

Implement Countable interface object

    <span>class</span> User <span>implements</span><span> Countable {
        </span><span>public</span> <span>function</span> <span>count</span><span>() {
            </span><span>return</span> 3<span>;
        }
    }

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

Run steps

<p>進(jìn)入switch語(yǔ)句檢測(cè)參數(shù)類型</p>
<p>　　如果是NULL，直接返回0</p>
<p>　　如果是數(shù)組，調(diào)用php_count_recursive函數(shù)機(jī)選數(shù)組元素個(gè)數(shù)</p>
<p>　　如果是對(duì)象，先檢查是否為數(shù)組對(duì)象（array-like object），如果是，則計(jì)算數(shù)組對(duì)象的數(shù)量</p>
<p>　　否則，如果對(duì)象實(shí)現(xiàn)了Countable接口，則調(diào)用Countable的count方法</p>
<p>　　最后，其他類型比如整型數(shù)組或字符串，都返回1。</p>

Source code interpretation

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

<p>如果當(dāng)前hash Bucket被遞歸訪問的次數(shù)大于1，說明重復(fù)遞歸，染回E_WARNING錯(cuò)誤</p>
<p>否則計(jì)算當(dāng)前數(shù)組層數(shù)的數(shù)組元素個(gè)數(shù)</p>
<p>如果有遞歸參數(shù)選項(xiàng)，則繼續(xù)遞歸訪問</p>

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, commonly known as 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 other 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. For example:
$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.

Original article with limited writing style and limited knowledge. If there is anything wrong in the article, please let me know.

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