php - 如果我不指定，数组元素的键是什么

Question

我想知道是否所有 PHP 数组的 value 都必须有 key？我不认为他们这样做，所以我的下一个问题是，每个 value 的 key 是否自动成为它在数组中的位置(基于 0 的索引)，或者否则 value 本身会变成 key 吗？

也许值只是没有键...好奇，因为如果没有键，我无法从 foreach 循环内的数组中删除元素。

Answer 1

I'm wondering if all PHP arrays have to have keys for their values?

是的。来自documentation :

Arrays

An array in PHP is actually an ordered map. A map is a type that associates values to keys.

因此，数组的所有元素都必须有一个键。

does the key for each value automatically become it's position in the array (0-based indexing)

几乎正确。如果一个元素没有指定键，则该键为1+前一个元素的键，第一个元素的键为0。

I can't delete an element from an array inside a foreach loop if it doesn't have a key.

实际上有foreach除值外还公开键的语法。来自documentation :

The foreach construct provides an easy way to iterate over arrays. foreach works only on arrays and objects, and will issue an error when you try to use it on a variable with a different data type or an uninitialized variable. There are two syntaxes:

foreach (array_expression as $value)
    statement
foreach (array_expression as $key => $value)
    statement

使用后一种foreach语法删除数组元素的例子如下:

// Remove elements from the array that are less than 10
foreach ($array as $key => $value) {
    if ($value < 10) {
        unset($array[$key]);
    }
}