array_shift()

(PHP 4, PHP 5, PHP 7)

将数组开头的单元移出数组

说明

array_shift()将$array的第一个单元移出并作为结果返回，将$array的长度减一并将所有其它单元向前移动一位。所有的数字键名将改为从零开始计数，文字键名将不变。

Note:使用此函数后会重置（reset()）array指针。

参数

输入的数组。

返回值

返回移出的值，如果$array为空或不是一个数组则返回NULL。

范例

Example #1array_shift()例子

以上例程会输出：

Array
(
    [0] => banana
    [1] => apple
    [2] => raspberry
)

并且orange被赋给了$fruit。

参见

• array_unshift() 在数组开头插入一个或多个单元
• array_push() 将一个或多个单元压入数组的末尾（入栈）
• array_pop() 弹出数组最后一个单元（出栈）

Using array_shift over larger array was fairly slow. It sped up as the array shrank, most likely as it has to reindex a smaller data set.
For my purpose, I used array_reverse, then array_pop, which doesn't need to reindex the array and will preserve keys if you want it to (didn't matter in my case). 
Using direct index references, i.e., array_test[$i], was fast, but direct index referencing + unset for destructive operations was about the same speed as array_reverse and array_pop. It also requires sequential numeric keys.

Notice:
the complexity of array_pop() is O(1). 
the complexity of array_shift() is O(n).
array_shift() requires a re-index process on the array, so it has to run over all the elements and index them.

Just a useful version which returns a simple array with the first key and value. Porbably a better way of doing it, but it works for me ;-)

Output:
Array
(
  [x] => ball
  [y] => hat
  [z] => apple
)
Array
(
  [x] => ball
)
Array
(
  [y] => hat
  [z] => apple
)

Here is a little function if you would like to get the top element and rotate the array afterwards.
function array_rotate(&$arr)
{
 $elm = array_shift($arr);
 array_push($arr, $elm);
 return $elm;
}

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