PHP replaces string only once

This is a method I found on the Internet. It is very good. Its function is: when string A appears in string B multiple times, it is used when we need to replace the first string A in string B with another string. For example, we need to use it to add links to keywords in the article content.

$needle=>String A,$replace=>The new string to replace string A with,$haystack=>String B;

Usage example: echo str_replace_once("Xiancheng.com","Xiancheng.com","Xiancheng.com—Xiancheng CSM official website");

function str_replace_once($needle, $replace, $haystack) {//只替换一次字符串
        $pos = strpos($haystack, $needle);
        if ($pos === false) {
            return $haystack;
        }
        return substr_replace($haystack, $replace, $pos, strlen($needle));
}