Understanding PHP parse_str() Function and Its Usage

When a PHP string contains multiple variable values (e.g., a URL query string), the parse_str() function can parse the string and assign each variable to a PHP variable or array.

The syntax of parse_str() is:

<code>parse_str(string $string, array &$result)</code>

Parameters:

$string : The input string to be parsed.

$result : If provided, the parsed variables are stored as elements of this array; starting with PHP 7.2, omitting this parameter is deprecated.

Return value: The function does not return a value.

Example 1 – Using the second parameter (recommended):

<code>&lt;?php
$str = "first=php&amp;arr[]=foobar&amp;arr[]=baz&amp;info=.cn";
parse_str($str, $output);

echo $output['first'];  // php
echo "&lt;br&gt;";

echo $output['arr'][0]; // foobar
echo "&lt;br&gt;";

echo $output['arr'][1]; // baz
echo "&lt;br&gt;";

echo $output['info'];   // .cn
echo "&lt;br&gt;";
print_r($output);
?>
</code>

The output will be:

<code>php
foobar
baz
.cn
Array ( [first] => php [arr] => Array ( [0] => foobar [1] => baz ) [info] => .cn )</code>

Example 2 – Using only one parameter (deprecated in PHP 7.2):

<code>&lt;?php
$str = "first=php&amp;arr[]=foobar&amp;arr[]=baz&amp;info=.cn";
parse_str($str);

echo $first . "&lt;br&gt;";

echo $arr[0] . "&lt;br&gt;";

echo $arr[1] . "&lt;br&gt;";

echo $info[0];
?>
</code>

In PHP 7.2, calling parse_str() without the second argument triggers an E_DEPRECATED warning, and in PHP 8.0 the $result argument becomes mandatory, so the single‑parameter usage is not recommended.