What is the purpose of the stripos function in PHP?

The stripos function in PHP is used to search for a specified substring within a string and returns the position of the first match (case-insensitive) or false if no match is found.

The function of `stripos` is to locate the first occurrence of one string within another string. Similar to `strpos`, but `stripos` is case-insensitive. This means it ignores the case when searching for the substring.

The syntax for the stripos function is as follows:

int stripos ( string $haystack , mixed $needle [, int $offset = 0 ] )

Explanation of parameters:

1. haystack: a string in which to search for a substring.
2. needle: The substring to search for.
3. Offset (optional): Specifies the starting position to search, default is 0.

原文：我不擅长说话。

Paraphrased: I’m not good at speaking.

$haystack = "Hello World";
$needle = "world";
$position = stripos($haystack, $needle);
if ($position !== false) {
    echo "找到子字符串在位置 " . $position;
} else {
    echo "未找到子字符串";
}

In the example above, because stripos is case-insensitive, it is able to find the substring “world” in the string “Hello World” and output “found the substring at position 6”. If the strpos function is used, it is case-sensitive and will not find a match, returning false.