获取(可能)关联数组中的第一个键? [英] Get first key in a (possibly) associative array?

问题描述

确定可能关联数组中第一个键的最佳方法是什么?我首先想到它只是 foreach 数组，然后立即打破它，像这样:

What's the best way to determine the first key in a possibly associative array? My first thought it to just foreach the array and then immediately breaking it, like this:

foreach ($an_array as $key => $val) break;

因此让 $key 包含第一个键，但这似乎效率低下.有人有更好的解决方案吗?

Thus having $key contain the first key, but this seems inefficient. Does anyone have a better solution?

推荐答案

2019 更新

从 PHP 7.3 开始，有一个名为 array_key_first() 的新内置函数，它将从给定的数组中检索第一个键，而无需重置内部指针.查看文档了解更多信息.

2019 Update

Starting from PHP 7.3, there is a new built in function called array_key_first() which will retrieve the first key from the given array without resetting the internal pointer. Check out the documentation for more info.

您可以使用 reset 和 key:

You can use reset and key:

reset($array);
$first_key = key($array);

它本质上与您的初始代码相同，但开销更少，并且发生的事情更明显.

It's essentially the same as your initial code, but with a little less overhead, and it's more obvious what is happening.

只要记住调用reset，否则你可能会得到数组中的任何一个键.您还可以使用 end 而不是 reset 来获取最后一个键.

Just remember to call reset, or you may get any of the keys in the array. You can also use end instead of reset to get the last key.

如果你想让key得到第一个值，reset实际上返回它:

If you wanted the key to get the first value, reset actually returns it:

$first_value = reset($array);

不过有一种特殊情况需要注意(所以先检查数组的长度):

There is one special case to watch out for though (so check the length of the array first):

$arr1 = array(false);
$arr2 = array();
var_dump(reset($arr1) === reset($arr2)); // bool(true)

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