count()

(PHP 4, PHP 5, PHP 7)

计算数组中的单元数目，或对象中的属性个数

说明

统计出数组里的所有元素的数量，或者对象里的东西。

对于对象，如果安装了SPL，可以通过实现Countable接口对count()挂钩（hook）。该接口只有一个方法Countable::count()，此方法为count()函数返回值。

关于 PHP 中如何实现和使用数组可以参考手册中数组章节中的详细描述。

参数

数组或者Countable对象。

如果可选的$mode参数设为COUNT_RECURSIVE（或 1），count()将递归地对数组计数。对计算多维数组的所有单元尤其有用。

count()能检测递归来避免无限循环，但每次出现时会产生E_WARNING错误（如果 array 不止一次包含了自身）并返回大于预期的统计数字。

返回值

返回$array_or_countable中的单元数目。如果参数既不是数组，也不是实现Countable接口的对象，将返回1。有个例外：如果$array_or_countable是NULL则结果是0。

范例

Example #1count()例子

以上例程会输出：

int(3)
int(3)
Warning: count(): Parameter must be an array or an object that implements Countable in … on line 12 // PHP 7.2 起
int(0)
Warning: count(): Parameter must be an array or an object that implements Countable in … on line 14 // PHP 7.2 起
int(1)

递归count()例子

更新日志

参见

• is_array() 检测变量是否是数组
• isset() 检测变量是否已设置并且非 NULL
• empty() 检查一个变量是否为空
• strlen() 获取字符串长度

[Editor's note: array at from dot pl had pointed out that count() is a cheap operation; however, there's still the function call overhead.]
If you want to run through large arrays don't use count() function in the loops , its a over head in performance, copy the count() value into a variable and use that value in loops for a better performance.
Eg:
// Bad approach
for($i=0;$i
You can organize your code to ensure that the variable is an array, or you can extend the Countable so that you don't have to do this check.

My function returns the number of elements in array for multidimensional arrays subject to depth of array. (Almost COUNT_RECURSIVE, but you can point on which depth you want to plunge). 

You can not get collect sub array count when there is only one sub array in an array: 
$a = array ( array ('a','b','c','d'));
$b = array ( array ('a','b','c','d'), array ('e','f','g','h'));
echo count($a); // 4 NOT 1, expect 1
echo count($b); // 2,  expected

I actually find the following function more useful when it comes to multidimension arrays when you do not want all levels of the array tree.
// $limit is set to the number of recursions 

All the previous recursive count solutions with $depth option would not avoid infinite loops in case the array contains itself more than once.
Here's a working solution:

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