What will array_combine() handle if the key or value array is empty?

M66 2025-06-07

In PHP, the array_combine() function is used to combine two numbers into an associative array, where the value of one array is used as the key to the new array and the value of the other array is used as the value of the new array. Its basic syntax is as follows:

 array_combine(array $keys, array $values): array

where $keys is an array used as keys for the new array, and $values is an array used as the value of the new array.

1. The general behavior of array_combine()

array_combine() expects two arrays to be passed in, and the lengths of these two arrays should be the same. If the lengths of the two arrays are inconsistent, PHP will throw a warning and return false . This means we cannot merge an array of length 3 with an array of length 2.

For example:

 $keys = ['a', 'b', 'c'];
$values = [1, 2];

$result = array_combine($keys, $values);

The above code will throw a warning and return false because the length of the $keys array and the $values array are inconsistent.

2. Behavior when passing in an empty array

But what will array_combine() do if one of the passed arrays is an empty array (such as $keys or $values is empty)? Let's take a look at two situations.

2.1 The key array is empty

If the $keys array is empty and the $values array has a value, PHP will return an empty array and will not report an error. For example:

 $keys = [];
$values = [1, 2, 3];

$result = array_combine($keys, $values);
var_dump($result);

turn out:

 array(0) { }

At this time, although the $values array has a value, because the $keys array is empty, it is impossible to assign a key to the value, so an empty array is returned.

2.2 The value array is empty

If the $values array is empty and the $keys array has a value, PHP will also return an empty array. For example:

 $keys = ['a', 'b', 'c'];
$values = [];

$result = array_combine($keys, $values);
var_dump($result);

turn out:

 array(0) { }

In this case, although the $keys array has a value, an empty array is returned because there is no corresponding value available for allocation.

3. Combination of empty arrays: Summary

To sum up, no matter whether the key array or the value array is empty, array_combine() will not report an error, but will return an empty array. It does not throw warnings or errors like it does when the array length is inconsistent.

This behavior makes array_combine() more robust when dealing with empty arrays because it avoids program crashing due to errors. However, when using this function, developers still need to ensure that the incoming array length is consistent and not empty, so as to avoid returning an empty array and failing to achieve the expected effect.

4. Use scenarios and suggestions

In actual development, we can avoid this by checking whether the array is empty. For example, you can use the empty() function to check whether the array is empty:

 if (!empty($keys) && !empty($values) && count($keys) === count($values)) {
    $result = array_combine($keys, $values);
} else {
    // Handle empty arrays
    echo "The array is empty or the length is inconsistent";
}

This avoids returning an empty array due to the empty array or inconsistent length.

By understanding the behavior of array_combine() , we can better handle various possible situations and ensure the robustness and maintainability of the code.

The above is a detailed analysis of array_combine() processing empty arrays. If you have other questions or need further discussion, please visit our website!

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