Use is_array to resolve common errors in array type judgment in PHP

gitbox 2025-05-29

In PHP development, we often need to determine whether a variable is an array. The is_array() function is one of the most commonly used tools. It seems simple, but it actually hides traps. This article will conduct in-depth analysis of the use of is_array() , common misunderstandings, and how to avoid traps.

Basic usage

is_array() is a built-in function with the following syntax:

 is_array(mixed $value): bool

It receives a variable as a parameter, which returns true if the variable is of array type, otherwise false .

Example:

 $data = [1, 2, 3];

if (is_array($data)) {
    echo "This is an array";
} else {
    echo "This is not an array";
}

Output:

 This is an array

Common Mistakes

1. Ignore type conversion

Some developers think that as long as the structure is similar to an array, it can be judged as an array by is_array() , but PHP does not automatically treat array-like strings, objects, etc. as arrays.

Error example:

 $data = '{"a":1,"b":2}'; // JSON String

if (is_array($data)) {
    echo "This is an array";
}

This code does not output "This is an array" because $data is a string type.

Solution:

 $data = json_decode('{"a":1,"b":2}', true); // The second parameter is set to true，Returns the associative array

if (is_array($data)) {
    echo "This is an array";
}

2. Ignore the judgment of empty arrays

Empty arrays are also arrays:

 $data = [];

if (is_array($data)) {
    echo "Still an array";
}

Many people tend to misjudgment "empty array" as "invalid data", and thus write the following error code:

 if ($data && is_array($data)) {
    // ...
}

If $data is an empty array, the above judgment is false , causing the program to not enter the logical block. The correct way is to judge the type first, and then determine whether it is empty:

 if (is_array($data) && !empty($data)) {
    // ...
}

Examples of usage scenarios

1. Safe Read Configuration

When reading the configuration file, first determine whether it is an array to prevent the program from crashing:

 $config = include 'https://gitbox.net/config.php';

if (!is_array($config)) {
    throw new Exception("Incorrect configuration file format！");
}

2. Process form data

When the form has array fields, it is recommended to always make type judgment:

 $tags = $_POST['tags'] ?? [];

if (is_array($tags)) {
    foreach ($tags as $tag) {
        echo htmlspecialchars($tag);
    }
}

Alternative: Type declaration + Type checking

In modern PHP, using type declarations is a more elegant way:

 function processData(array $items) {
    foreach ($items as $item) {
        // Processing logic
    }
}

This not only reduces the frequency of manually calling is_array() , but also improves the robustness of the code.

Summarize

Although is_array() is a simple function, its incorrect usage may lead to program logic deviations or even errors. We should:

To know clearly the source and expected type of variables;
First parse the structure data such as JSON;
Do appropriate processing of empty arrays;
If possible, use a type declaration instead of runtime checking.

Only by truly understanding how is_array() works can you write more robust and maintainable PHP code.

is_array