Understanding the http_build_query() Function in PHP

The http_build_query() function in PHP is used to generate a URL-encoded query string from an associative array or an object. This function is particularly useful when you need to pass parameters via a URL or submit data in a form where URL encoding is required.

When you need to send data in a URL format, especially for making API calls or creating links with query parameters, the http_build_query() function simplifies this process by converting data into a string that can be appended to URLs. It's also commonly used when working with HTTP GET requests or forms.

Syntax of http_build_query()

http_build_query($data, $prefix = '', $arg_separator = '&', $enc_type = PHP_QUERY_RFC1738)

Parameters:

• $data: The data to be encoded. It can be an associative array, an indexed array, or an object.
• $prefix (Optional): A prefix for the query string. If provided, this prefix will be added before the parameter names.
• $arg_separator (Optional): A separator between arguments. The default is &, but you can specify another character like ;.
• $enc_type (Optional): This defines the encoding type. It defaults to PHP_QUERY_RFC1738, which encodes spaces as %20. Alternatively, you can use PHP_QUERY_RFC3986 for encoding spaces as +.

Example 1: Basic Usage with Associative Array

<?php
$data = array('name' => 'John Doe', 'age' => 30, 'city' => 'New York');
$queryString = http_build_query($data);
echo $queryString;
?>

Output:

name=John+Doe&age=30&city=New+York

In this example, we created an associative array with name, age, and city as keys. The http_build_query() function converts this array into a query string that can be appended to a URL.

Example 2: URL Encoding with Custom Separator

<?php
$data = array('name' => 'Alice', 'job' => 'Engineer', 'location' => 'London');
$queryString = http_build_query($data, '', ';');
echo $queryString;
?>

Output:

name=Alice;job=Engineer;location=London

Here, we specified a custom separator ; instead of the default &. This allows you to customize how the parameters are joined in the query string.

Example 3: Using Prefix for Nested Arrays

<?php
$data = array('user' => array('name' => 'Bob', 'email' => 'bob@example.com'));
$queryString = http_build_query($data, 'data_');
echo $queryString;
?>

Output:

data_user%5Bname%5D=Bob&data_user%5Bemail%5D=bob%40example.com

In this example, a prefix (data_) is added to each parameter, and nested arrays are encoded correctly.

Example 4: URL Encoding with Objects

<?php
class User {
    public $name = 'Eve';
    public $age = 28;
}
$user = new User();
$queryString = http_build_query($user);
echo $queryString;
?>

Output:

name=Eve&age=28

Objects can also be passed to http_build_query(), and their public properties are encoded in the query string.