如何取得 Foreach 迴圈中元素的索引？

Identifying foreach Loop Indices

In many programming scenarios, it becomes necessary to track the iteration index within a loop. While traditional for loops explicitly provide the iteration variable, determining the index in a foreach loop can be more elusive.

Can foreach Loops Provide Indices?

Unlike for loops, which increment a variable with each iteration, foreach loops do not naturally expose an index. Instead, they iterate over the elements of an iterable (such as an array) and assign each element to the specified variable.

Accessing foreach Loop Indices

However, despite their inherent lack of index exposure, foreach loops do offer a solution for obtaining the current index. The solution lies in utilizing a built-in array function:

foreach($array as $key => $value) {
    // Do something with $key (the index) and $value (the value)
}

In this PHP example, $key becomes the associative index of each element in the $array. As the loop iterates, $key incrementally indicates the index of the current element. This technique is applicable to any iterable that adheres to the Traversable interface.

Additional Notes:

• It's important to understand that $key is not a true numeric index. It represents the associative key of the element, which may or may not be numeric.
• If the iterable does not have associated keys (i.e., it is an indexed array), $key will be automatically assigned numeric indices starting from 0.

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