What is the difference between strstr() and strpos() functions in PHP and when should each be used?

The difference between strstr() and strpos() functions in PHP is that strstr() returns the substring starting from the first occurrence of a needle within a haystack, while strpos() returns the position of the first occurrence of a needle within a haystack. Use strstr() when you need to extract a substring starting from the first occurrence of a specific character or string within a larger string. Use strpos() when you only need to find the position of a specific character or string within a larger string.

// Using strstr()
$haystack = "Hello, World!";
$needle = ",";
$substring = strstr($haystack, $needle);
echo $substring; // Output: ", World!"

// Using strpos()
$haystack = "Hello, World!";
$needle = ",";
$position = strpos($haystack, $needle);
echo $position; // Output: 6