How does the http_build_query function handle complex nested array structures? Any useful tips?

gitbox 2025-09-20

<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-comment">// This part is an unrelated PHP code example</span></span><span>
</span><span><span class="hljs-variable">$example</span></span><span> = [</span><span><span class="hljs-string">"title"</span></span><span> => </span><span><span class="hljs-string">"PHP Article"</span></span><span>, </span><span><span class="hljs-string">"date"</span></span><span> => </span><span><span class="hljs-title function_ invoke__">date</span></span><span>(</span><span><span class="hljs-string">"Y-m-d"</span></span><span>)];
</span><span><span class="hljs-title function_ invoke__">print_r</span></span><span>(</span><span><span class="hljs-variable">$example</span></span><span>);
<p></span>?></p>
<p><hr></p>
<p><?php<br>
// Main content starts<br>
echo "<h1>How does the http_build_query function handle complex nested array structures? Any useful tips?</h1>";</p>
<p>echo <span><span class="hljs-string">"<p>In PHP, <code>http_build_query()

echo "

2. Handling nested arrays

";
echo "

When the array contains nested arrays, http_build_query() uses square brackets to represent hierarchy:

echo '

'</span></span><span>;<br>
</span><span><span>echo</span></span><span> <span>'```php<br>
$data = [<br>
"user" => [<br>
"name" => "Alice",<br>
"email" => "<a class="decorated-link cursor-pointer" rel="noopener">[email protected]<span aria-hidden="true" class="ms-0.5 inline-block align-middle leading-none"><svg width="20" height="20" viewBox="0 0 20 20" fill="currentColor" xmlns="http://www.w3.org/2000/svg" data-rtl-flip="" class="block h-[0.75em] w-[0.75em] stroke-current stroke-[0.75]"><path d="M14.3349 13.3301V6.60645L5.47065 15.4707C5.21095 15.7304 4.78895 15.7304 4.52925 15.4707C4.26955 15.211 4.26955 14.789 4.52925 14.5293L13.3935 5.66504H6.66011C6.29284 5.66504 5.99507 5.36727 5.99507 5C5.99507 4.63273 6.29284 4.33496 6.66011 4.33496H14.9999L15.1337 4.34863C15.4369 4.41057 15.665 4.67857 15.665 5V13.3301C15.6649 13.6973 15.3672 13.9951 14.9999 13.9951C14.6327 13.9951 14.335 13.6973 14.3349 13.3301Z"></path></svg></span></a>"<br>
],<br>
"tags" => ["php", "web"]<br>
];<br>
$query = http_build_query($data);<br>
echo $query;<br>
// Output: user%5Bname%5D=Alice&user%5Bemail%5D=alice%40example.com&tags%5B0%5D=php&tags%5B1%5D=web</p>
<pre class="overflow-visible!" data-is-last-node=""><div class="contain-inline-size rounded-2xl relative bg-token-sidebar-surface-primary"><div class="flex items-center text-token-text-secondary px-4 py-2 text-xs font-sans justify-between h-9 bg-token-sidebar-surface-primary select-none rounded-t-2xl">'</span>;</div><div class="sticky top-9"><div class="absolute end-0 bottom-0 flex h-9 items-center pe-2"><div class="bg-token-bg-elevated-secondary text-token-text-secondary flex items-center gap-4 rounded-sm px-2 font-sans text-xs"><button class="flex gap-1 items-center select-none py-1" aria-label="复制"><svg width="20" height="20" viewBox="0 0 20 20" fill="currentColor" xmlns="http://www.w3.org/2000/svg" class="icon-sm"><path d="M12.668 10.667C12.668 9.95614 12.668 9.46258 12.6367 9.0791C12.6137 8.79732 12.5758 8.60761 12.5244 8.46387L12.4688 8.33399C12.3148 8.03193 12.0803 7.77885 11.793 7.60254L11.666 7.53125C11.508 7.45087 11.2963 7.39395 10.9209 7.36328C10.5374 7.33197 10.0439 7.33203 9.33301 7.33203H6.5C5.78896 7.33203 5.29563 7.33195 4.91211 7.36328C4.63016 7.38632 4.44065 7.42413 4.29688 7.47559L4.16699 7.53125C3.86488 7.68518 3.61186 7.9196 3.43555 8.20703L3.36524 8.33399C3.28478 8.49198 3.22795 8.70352 3.19727 9.0791C3.16595 9.46259 3.16504 9.95611 3.16504 10.667V13.5C3.16504 14.211 3.16593 14.7044 3.19727 15.0879C3.22797 15.4636 3.28473 15.675 3.36524 15.833L3.43555 15.959C3.61186 16.2466 3.86474 16.4807 4.16699 16.6348L4.29688 16.6914C4.44063 16.7428 4.63025 16.7797 4.91211 16.8027C5.29563 16.8341 5.78896 16.835 6.5 16.835H9.33301C10.0439 16.835 10.5374 16.8341 10.9209 16.8027C11.2965 16.772 11.508 16.7152 11.666 16.6348L11.793 16.5645C12.0804 16.3881 12.3148 16.1351 12.4688 15.833L12.5244 15.7031C12.5759 15.5594 12.6137 15.3698 12.6367 15.0879C12.6681 14.7044 12.668 14.211 12.668 13.5V10.667ZM13.998 12.665C14.4528 12.6634 14.8011 12.6602 15.0879 12.6367C15.4635 12.606 15.675 12.5492 15.833 12.4688L15.959 12.3975C16.2466 12.2211 16.4808 11.9682 16.6348 11.666L16.6914 11.5361C16.7428 11.3924 16.7797 11.2026 16.8027 10.9209C16.8341 10.5374 16.835 10.0439 16.835 9.33301V6.5C16.835 5.78896 16.8341 5.29563 16.8027 4.91211C16.7797 4.63025 16.7428 4.44063 16.6914 4.29688L16.6348 4.16699C16.4807 3.86474 16.2466 3.61186 15.959 3.43555L15.833 3.36524C15.675 3.28473 15.4636 3.22797 15.0879 3.19727C14.7044 3.16593 14.211 3.16504 13.5 3.16504H10.667C9.9561 3.16504 9.46259 3.16595 9.0791 3.19727C8.79739 3.22028 8.6076 3.2572 8.46387 3.30859L8.33399 3.36524C8.03176 3.51923 7.77886 3.75343 7.60254 4.04102L7.53125 4.16699C7.4508 4.32498 7.39397 4.53655 7.36328 4.91211C7.33985 5.19893 7.33562 5.54719 7.33399 6.00195H9.33301C10.022 6.00195 10.5791 6.00131 11.0293 6.03809C11.4873 6.07551 11.8937 6.15471 12.2705 6.34668L12.4883 6.46875C12.984 6.7728 13.3878 7.20854 13.6533 7.72949L13.7197 7.87207C13.8642 8.20859 13.9292 8.56974 13.9619 8.9707C13.9987 9.42092 13.998 9.97799 13.998 10.667V12.665ZM18.165 9.33301C18.165 10.022 18.1657 10.5791 18.1289 11.0293C18.0961 11.4302 18.0311 11.7914 17.8867 12.1279L17.8203 12.2705C17.5549 12.7914 17.1509 13.2272 16.6553 13.5313L16.4365 13.6533C16.0599 13.8452 15.6541 13.9245 15.1963 13.9619C14.8593 13.9895 14.4624 13.9935 13.9951 13.9951C13.9935 14.4624 13.9895 14.8593 13.9619 15.1963C13.9292 15.597 13.864 15.9576 13.7197 16.2939L13.6533 16.4365C13.3878 16.9576 12.9841 17.3941 12.4883 17.6982L12.2705 17.8203C11.8937 18.0123 11.4873 18.0915 11.0293 18.1289C10.5791 18.1657 10.022 18.165 9.33301 18.165H6.5C5.81091 18.165 5.25395 18.1657 4.80371 18.1289C4.40306 18.0962 4.04235 18.031 3.70606 17.8867L3.56348 17.8203C3.04244 17.5548 2.60585 17.151 2.30176 16.6553L2.17969 16.4365C1.98788 16.0599 1.90851 15.6541 1.87109 15.1963C1.83431 14.746 1.83496 14.1891 1.83496 13.5V10.667C1.83496 9.978 1.83432 9.42091 1.87109 8.9707C1.90851 8.5127 1.98772 8.10625 2.17969 7.72949L2.30176 7.51172C2.60586 7.0159 3.04236 6.6122 3.56348 6.34668L3.70606 6.28027C4.04237 6.136 4.40303 6.07083 4.80371 6.03809C5.14051 6.01057 5.53708 6.00551 6.00391 6.00391C6.00551 5.53708 6.01057 5.14051 6.03809 4.80371C6.0755 4.34588 6.15483 3.94012 6.34668 3.56348L6.46875 3.34473C6.77282 2.84912 7.20856 2.44514 7.72949 2.17969L7.87207 2.11328C8.20855 1.96886 8.56979 1.90385 8.9707 1.87109C9.42091 1.83432 9.978 1.83496 10.667 1.83496H13.5C14.1891 1.83496 14.746 1.83431 15.1963 1.87109C15.6541 1.90851 16.0599 1.98788 16.4365 2.17969L16.6553 2.30176C17.151 2.60585 17.5548 3.04244 17.8203 3.56348L17.8867 3.70606C18.031 4.04235 18.0962 4.40306 18.1289 4.80371C18.1657 5.25395 18.165 5.81091 18.165 6.5V9.33301Z"></path></svg>复制代码</button></div></div></div><div class="overflow-y-auto p-4" dir="ltr">echo '

';

echo "As you can see, keys in nested arrays are automatically converted into formats like user[name] and tags[0], and are URL-encoded.";

echo "3. Using arg_separator and numeric_prefix";
echo "The function prototype allows passing a second and third parameter:";

echo '';
echo '```php
http_build_query(array $query_data, string $numeric_prefix = "", string $arg_separator = "&", int $encoding_type = PHP_QUERY_RFC1738): string
```';
echo '';

echo "- numeric_prefix: When array keys are numeric, you can add a prefix.

- arg_separator: Defines the separator between different parameters (default is &).";

echo "4. Tips to avoid overly deep array nesting";
echo "
When generating URLs, if the nesting is too deep, consider using json_encode() to convert complex arrays into JSON before sending to the backend.
You can write a custom function to flatten multi-dimensional arrays before calling http_build_query(), avoiding overly long query strings.
Using PHP_QUERY_RFC3986 as the encoding_type parameter produces URLs encoded according to RFC 3986, which may suit certain APIs better.
";

echo "5. Example: Flattening nested arrays";

echo '';
echo '```php
function flatten_array($array, $prefix = "") {
    $result = [];
    foreach ($array as $key => $value) {
        $new_key = $prefix === "" ? $key : $prefix . "[" . $key . "]";
        if (is_array($value)) {
            $result = array_merge($result, flatten_array($value, $new_key));
        } else {
            $result[$new_key] = $value;
        }
    }
    return $result;
}

$data = [
    "user" => ["name" => "Alice", "email" => "[email protected]"],
    "tags" => ["php", "web"]
];

$query = http_build_query(flatten_array($data));
echo $query;
// Output: user[name]=Alice&user[email][email protected]&tags[0]=php&tags[1]=web
```';
echo '';

echo "By flattening the array, we gain more flexibility in controlling the final query string format.";

echo "Conclusion";
echo "http_build_query() is a powerful tool for handling URL query parameters, but when working with complex nested arrays, it’s important to understand how it encodes data. If needed, you can flatten arrays, use JSON, or adjust encoding methods to ensure data transmission is correct and readable.";
?>