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PHP JSON

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In modern web development, data exchange between the server and client is essential. One of the most common formats for this purpose is JSON (JavaScript Object Notation). PHP provides built-in functions to encode and decode JSON, making it simple to work with structured data. Understanding PHP JSON handling is important for tasks like API development, AJAX requests, and storing configuration or structured data.

What is JSON?

JSON is a lightweight data-interchange format that is easy for humans to read and write and easy for machines to parse and generate. It represents data using key-value pairs and arrays. JSON is language-independent, but it is most commonly associated with JavaScript.

Example of a JSON object:

{
    "name": "Alice",
    "email": "alice@example.com",
    "age": 25,
    "skills": ["PHP", "JavaScript", "HTML"]
}

In PHP, JSON data can be converted to associative arrays or objects, which makes it convenient to work with.

PHP Functions for JSON

PHP provides two main functions to work with JSON:

  1. json_encode() – Converts PHP arrays or objects into a JSON string.

  2. json_decode() – Converts a JSON string into a PHP variable (array or object).

Encoding PHP Data to JSON

The json_encode() function takes a PHP array or object and returns a JSON string.

Example with an associative array:

$user = array(
    "name" => "Alice",
    "email" => "alice@example.com",
    "age" => 25,
    "skills" => array("PHP", "JavaScript", "HTML")
);

$json = json_encode($user);
echo $json;

Output:

{"name":"Alice","email":"alice@example.com","age":25,"skills":["PHP","JavaScript","HTML"]}

You can also encode objects:

class User {
    public $name = "Bob";
    public $email = "bob@example.com";
    public $age = 30;
}

$user = new User();
echo json_encode($user);

This will output a JSON representation of the object.

Decoding JSON to PHP

The json_decode() function converts a JSON string into a PHP variable. By default, it returns an object. You can pass true as the second parameter to get an associative array instead.

Example:

$json = '{"name":"Alice","email":"alice@example.com","age":25,"skills":["PHP","JavaScript","HTML"]}';

// Decode as object
$user = json_decode($json);
echo $user->name; // Outputs: Alice

// Decode as associative array
$userArray = json_decode($json, true);
echo $userArray['email']; // Outputs: alice@example.com

Handling Errors

When working with JSON, errors can occur if the string is malformed. PHP provides the json_last_error() function to check for errors and json_last_error_msg() to get a descriptive message.

Example:

$json = '{"name":"Alice","email":"alice@example.com",age:25}'; // Invalid JSON

$data = json_decode($json);

if (json_last_error() !== JSON_ERROR_NONE) {
    echo "JSON Error: " . json_last_error_msg();
}

This helps identify problems like missing quotes, trailing commas, or other syntax issues.

JSON and Arrays

JSON handles arrays and nested arrays easily.

Example:

$users = array(
    array("name" => "Alice", "age" => 25),
    array("name" => "Bob", "age" => 30)
);

echo json_encode($users);

Output:

[{"name":"Alice","age":25},{"name":"Bob","age":30}]

Nested arrays are useful for representing structured data, like lists of products or user records.

Options in JSON Encoding

The json_encode() function provides options to modify output:

  • JSON_PRETTY_PRINT – Formats JSON in a human-readable way with indentation.

  • JSON_UNESCAPED_UNICODE – Preserves Unicode characters without escaping.

  • JSON_UNESCAPED_SLASHES – Keeps forward slashes / unescaped.

  • JSON_NUMERIC_CHECK – Converts numeric strings to numbers.

Example:

$data = array("name" => "Alice", "email" => "alice@example.com", "age" => "25");

echo json_encode($data, JSON_PRETTY_PRINT | JSON_NUMERIC_CHECK);

Output:

{
    "name": "Alice",
    "email": "alice@example.com",
    "age": 25
}

This is more readable and ensures numeric strings are converted to numbers.

Practical Use Case: AJAX Response

JSON is widely used in web applications to send data between the server and client asynchronously.

Example PHP script returning JSON:

header('Content-Type: application/json');

$response = array(
    "status" => "success",
    "message" => "Data retrieved successfully",
    "data" => array("name" => "Alice", "age" => 25)
);

echo json_encode($response);

The client-side JavaScript can easily parse this JSON and display it on a webpage.

Summary of the Tutorial

PHP JSON functions provide an easy way to encode and decode structured data. json_encode() converts PHP arrays or objects into JSON strings, while json_decode() converts JSON strings back into PHP variables. Advanced features like options for pretty print, Unicode handling, and numeric conversion help control output format. By combining error handling and nested structures, PHP JSON functions allow developers to work efficiently with APIs, AJAX, and structured data exchange.

Practice Questions

  1. Write a PHP script to convert an associative array containing user information (name, email, age) into a JSON string.

  2. Create a PHP script that decodes a JSON string representing a product (name, price, category) and prints each value separately.

  3. Write a PHP program to encode an array of multiple users into JSON and format it using JSON_PRETTY_PRINT.

  4. Implement a PHP script to decode a JSON string into an associative array and check for errors using json_last_error() and json_last_error_msg().

  5. Create a PHP script that encodes a PHP object representing a blog post (title, author, content) into JSON.

  6. Write a PHP program to encode numeric strings in an array as numbers using JSON_NUMERIC_CHECK.

  7. Implement a PHP script that decodes a nested JSON string (users with multiple addresses) into a PHP variable and accesses a specific nested value.

  8. Write a PHP script that returns a JSON response for an AJAX request containing status, message, and data fields.

  9. Create a PHP script to decode a JSON string containing Unicode characters, ensuring the characters are correctly preserved in the output.

  10. Write a PHP program to combine json_encode() options (JSON_PRETTY_PRINT and JSON_UNESCAPED_SLASHES) while encoding an array representing website URLs.

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