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이 문서에서는 PHP 중국어 웹사이트 매뉴얼 풀어 주다
(PHP 4, PHP 5, PHP 7)
count — 计算数组中的单元数目或对象中的属性个数
$var
[, int $mode
= COUNT_NORMAL
] )统计一个数组里的所有元素,或者一个对象里的东西。
对于对象,如果安装了 SPL,可以通过实现 Countable 接口来调用 count() 。该接口只有一个方法 Countable::count() ,此方法返回 count() 函数的返回值。
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。
var
数组或者对象。
mode
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。mode
的默认值是 0。 count()
识别不了无限递归。
返回 var
中的单元数目。
如果 var
不是数组类型或者实现了
Countable 接口的对象,将返回
1,有一个例外,如果
var
是 NULL
则结果是 0。
count() 对没有初始化的变量返回 0,但对于空的数组也会返回 0。用 isset() 来测试变量是否已经初始化。
版本 | 说明 |
---|---|
4.2.0 |
添加了可选的 mode 参数。
|
Example #1 count() 例子
<?php
$a [ 0 ] = 1 ;
$a [ 1 ] = 3 ;
$a [ 2 ] = 5 ;
$result = count ( $a );
// $result == 3
$b [ 0 ] = 7 ;
$b [ 5 ] = 9 ;
$b [ 10 ] = 11 ;
$result = count ( $b );
// $result == 3
$result = count ( null );
// $result == 0
$result = count ( false );
// $result == 1
?>
Example #2 递归 count() 例子
<?php
$food = array( 'fruits' => array( 'orange' , 'banana' , 'apple' ),
'veggie' => array( 'carrot' , 'collard' , 'pea' ));
// recursive count
echo count ( $food , COUNT_RECURSIVE ); // output 8
// normal count
echo count ( $food ); // output 2
?>
[#1] pjrfigueiredo at gmail dot com [2015-07-14 12:27:52]
PHP - count an object returns 1?
This is how: $total = count((array)$objecto);
[#2] pied-pierre [2015-06-04 17:27:30]
A function of one line to find the number of elements that are not arrays, recursively :
function count_elt($array, &$count=0){
foreach($array as $v) if(is_array($v)) count_elt($v,$count); else ++$count;
return $count;
}
[#3] JumpIfBelow [2015-05-05 14:18:43]
As I see in many codes, don't use count to iterate through array.
Onlyranga says you could declare a variable to store it before the for loop.
I agree with his/her approach, using count in the test should be used ONLY if you have to count the size of the array for each loop.
You can do it in the for loop too, so you don't have to "search" where the variable is set.
e.g.
<?php
$array = [1, 5, 'element'];
for($i = 0, $c = count($array); $i < $c; $i++)
var_dump($array[$i]);
?>
[#4] array at from dot pl [2015-02-19 22:22:43]
onlyranga at gmail dot com note about keeping count() in variable is not really correct, For some time now using variable and calling `count()` on each loop iteration costs you basically the same.
Proof: If you look into PHP sources then you see that for some time now it returns internal counter value instead of counting on each call. Here is `count` implementation: [1] where for array it calls `php_count_recursive` [2] which is then calls zend_hash_num_elements and returns `nNumOfElements` internal variable. It is not counting anything.
You may want to read this blog post about PHP internals too: https://nikic.github.io/2012/03/28/Understanding-PHPs-internal-array-implementation.html
[1] https://github.com/php/php-src/blob/PHP-5.5/ext/standard/array.c#L306
[2] https://github.com/php/php-src/blob/e10e151e9b92313a7085272c85bebf6c82017fce/ext/standard/array.c#L264
[#5] jingsoft at 126 dot com [2015-01-07 09:34:34]
There is an array:
$array = array ( 1, array( 1, 2, 3));
use count($array) will return 5, is a bug?
[#6] softontherocks at gmail dot com [2014-10-31 19:45:37]
I posted in my blog a small article talking about this function. If you want to visit it look at this url:
http://softontherocks.blogspot.com/2014/10/contar-los-elementos-de-un-array-en-php.html
[#7] onlyranga at gmail dot com [2014-04-28 02:14:32]
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<count($some_arr);$i++)
{
// calculations
}
// Good approach
$arr_length = count($some_arr);
for($i=0;$i<$arr_length;$i++)
{
// calculations
}
[#8] norbyte [2014-02-26 12:06:32]
If you want to check whether large arrays contain a specific (less) number of array elements, don't use count(). This is very slow because each element has to get iterated.
This is much faster:
function isArrayCount(array $array, $count) {
$count = (int) $count;
$result = reset($array);
if ($count === 0) {
// for empty arrays reset returns FALSE
// we have to switch the boolean result
$result = !$result;
}
for($i = 1; $i < $count; $i++) {
if (next($array) === FALSE) {
$result = FALSE;
break;
}
}
return $result;
}
[#9] Gerd Christian Kunze [2013-12-11 12:56:19]
Get maxWidth and maxHeight of a two dimensional array..?
Note:
1st dimension = Y (height)
2nd dimension = X (width)
e.g. rows and cols in database result arrays
<?php
$TwoDimensionalArray = array( 0 => array( 'key' => 'value', ...), ... );
?>
So for Y (maxHeight)
<?php
$maxHeight = count( $TwoDimensionalArray )
?>
And for X (maxWidth)
<?php
$maxWidth = max( array_map( 'count', $TwoDimensionalArray ) );
?>
Simple? ;-)
[#10] MaxTheDragon at home dot nl [2013-11-06 13:21:31]
If you wish to test if an array contains any elements (or is empty), you might tempted to use count to do something like this:
<?php
if (count($my_array) > 0) {
// array is not empty...
}
// or this ...
if (count($my_array) === 0) {
// array is empty...
}
?>
Using the count function here is totally unnecessary and slower.
Instead, you should rely on the fact that empty arrays evaluate to false when cast to a boolean:
<?php
$hasElements = (boolean) $my_array;
// or ...
$isEmpty = !$my_array;
// or in a conditional statement...
if ($my_array) {
// array is not empty...
}
?>
Only use count if you need to know if an array contains a specific number of elements n (where n > 0).
[#11] lopezvit at gmail dot com [2013-10-10 17:54:12]
I think that maybe that is faster (I don't know why, because, at least in C, for loops are faster than while ones due to compile optimization) but what is sure is that, in case the list is empty, you are going to iterate over the loop at least one. And I'm sure that is not what you want to do. The correct way in this occassion is to use a normal while, not a do, while.
[#12] me at me dot com [2013-09-07 14:58:29]
To the poster above, the fastest way is to use 'do/while'. Try this way, you will find it faster than 'for'.
$arrayCount = count($array);
do{
// some code here
--$arrayCount;
}
while($arrayCount > 0);
[#13] semmelbroesel at gmail dot com [2013-08-15 14:14:28]
I've read this somewhere else before, but experienced it first hand now, so I thought I'd post it here.
While in regular use, count() is pretty fast, this changes rapidly when used in a for loop. Example:
for ($x = 0; $x < count($array); $x++)
{
// some code here
}
If your array contains a lot of data, this code gets slowed down significantly. Better way to write this:
$arrayCount = count($array);
for ($x = 0; $x < $arrayCount; $x++)
{
// some code here
}
I didn't think it would make such a difference, but it did in my case - changed 15 seconds load time into 1 second!
[#14] nicolas dot grekas+php at gmail dot com [2011-09-10 11:29:18]
As of PHP 5.2.6, count() DOES detect infinite recursion.
It triggers a warning when its argument is a recursive array.
[#15] jezdec at email dot cz [2009-04-19 16:42:37]
Hi there,
there is a simple script with example for counting rows and columns of a two-dimensional array.
<?php
$data = array(
"apples" =>
array("red", "yellow", "pineapples"),
"bananas" =>
array("small", "medium", "big"),
"vegs" =>
array("potatoes", "carrots", "onions")
);
$rows = count($data,0);
$cols = (count($data,1)/count($data,0))-1;
print "There are {$rows} rows and {$cols} columns in the table!";
?>
[#16] atoi_monte at hotmail dot com [2007-06-28 14:10:13]
Please note: While SPL is compiled into PHP by default starting with PHP 5, the Countable interface is not available until 5.1
[#17] danny at dannymendel dot com [2007-06-13 13:14:43]
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.
// $limit is set to the number of recursions
<?php
function count_recursive ($array, $limit) {
$count = 0;
foreach ($array as $id => $_array) {
if (is_array ($_array) && $limit > 0) {
$count += count_recursive ($_array, $limit - 1);
} else {
$count += 1;
}
}
return $count;
}
?>
[#18] alexandr at vladykin dot pp dot ru [2006-11-08 04:28:14]
My function returns the number of elements in array for multidimensional arrays subject to depth of array. (Almost COUNT_RECURSIVE, but you can point on which depth you want to plunge).
<?php
function getArrCount ($arr, $depth=1) {
if (!is_array($arr) || !$depth) return 0;
$res=count($arr);
foreach ($arr as $in_ar)
$res+=getArrCount($in_ar, $depth-1);
return $res;
}
?>
[#19] freefaler at gmail dot com [2004-11-19 17:01:53]
If you want to count only elements in the second level of 2D arrays.A close to mind note, useful for multidimentional arrays:
<?php
$food = array('fruits' => array('orange', 'banana', 'apple'),
'veggie' => array('carrot', 'collard','pea'));
// recursive count
echo count($food,COUNT_RECURSIVE); // output 8
// normal count
echo count($food); // output 2
// all the fruits and veggies
echo (count($food,COUNT_RECURSIVE)-count($food,0)); //output 6
?>