How to use array_fill() elegantly during an interview?

M66 2025-06-05

In PHP's standard library functions, array_fill() is a small but very practical tool. During interviews, candidates are often examined whether they are familiar with this seemingly simple but ingenious function. Understanding and mastering the use of array_fill() can not only improve efficiency in actual development, but also demonstrate your proficiency in array processing in interviews.

1. The basic usage of array_fill()

array_fill() is used to fill an array with the specified value. The function prototype is as follows:

 array array_fill ( int $start_index , int $count , mixed $value )

$start_index : Start index
$count : Number of elements
$value : The value used for filling

Example:

 $array = array_fill(0, 5, 'PHP');
print_r($array);

Output:

 Array
(
    [0] => PHP
    [1] => PHP
    [2] => PHP
    [3] => PHP
    [4] => PHP
)

This function is very convenient when you need to quickly create an array with default values.

2. Analysis of application scenarios

1. Initialize the data structure

For example, you want to initialize a set of boolean arrays with a state of false :

 $status = array_fill(0, 10, false);

Suitable for initialization tasks such as: user voting status, permission check mark, question answering status, etc.

2. Placeholder array or fill data

Sometimes we process external data, some field values are missing, but we want to maintain a unified data format. At this time, you can use array_fill() to occupy the place.

 $placeholders = array_fill(0, 3, 'N/A');

This writing is very common when exporting CSVs or building a unified data table.

3. Form default value

Suppose a questionnaire has 5 questions and the default value for each question is 0 points, you can write it like this:

 $scores = array_fill(1, 5, 0); // From the title number 1 start

3. Use in combination with other functions

Array_fill() combined with other array functions can implement more complex logic.

Joint with array_combine() :

If you have a set of field names, you want to assign a default value to each field:

 $fields = ['name', 'email', 'phone'];
$defaults = array_fill(0, count($fields), '');
$data = array_combine($fields, $defaults);

Output:

 Array
(
    [name] => 
    [email] => 
    [phone] => 
)

This is an excellent way to handle form default values, interface field formatting.

4. Processing of negative indexes

array_fill() allows negative indexing, which is useful in some specific logic but requires careful handling.

 $negArray = array_fill(-3, 3, 'X');

Output:

 Array
(
    [-3] => X
    [-2] => X
    [-1] => X
)

5. Simulation questions suggestions

During the interview, the interviewer may ask questions like this:

Use array_fill() to quickly generate an array with indexes ranging from 1 to 100 and initial values of 0, requiring that the key of the final array be a continuous integer.

Answer:

 $data = array_fill(1, 100, 0);

Advanced requirements may be: map all keys into string formats, such as 'item_1' to 'item_100' .

 $keys = array_map(fn($n) => "item_$n", range(1, 100));
$values = array_fill(0, 100, 0);
$result = array_combine($keys, $values);

6. Combining business logic examples: Bulk building interface data structures

Suppose we want to build a POST interface and submit an array of 10 user default information to https://api.m66.net/data , each user data format is:

 [
    'name' => '',
    'email' => '',
    'status' => 'inactive'
]

We can write this way:

 $defaultUser = [
    'name' => '',
    'email' => '',
    'status' => 'inactive'
];

$users = array_fill(0, 10, $defaultUser);

$payload = json_encode(['users' => $users]);

$ch = curl_init('https://api.m66.net/data');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ['Content-Type: application/json']);
curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);
$response = curl_exec($ch);
curl_close($ch);

This code shows how array_fill() can simplify the process of building structured data in real business scenarios.

Conclusion

Mastering the use of array_fill() can make your code more concise and intuitive. Although it is not complicated, it often hides "the interviewer's test points". Next time you encounter a need for initialization and default value filling, don't forget its existence. Using array_fill() gracefully is not only a plus at the code level, but also a highlight of the details that stand out in the interview.

array_fill