php字符串函数的使用

<?php

    //分别用substr、strpos、substr_compare
    //编写start_with、end_with函数

    function start1($haystack, $needle) {
        return substr($haystack, 0, mb_strlen($needle)) === $needle;
    }

    function start2($haystack, $needle) {
        return strpos($haystack, $needle) === 0;
    }

    function start3($haystack, $needle) {
        return substr_compare($haystack, $needle, 0, mb_strlen($needle)) === 0;
    }

    function end1($haystack, $needle) {
        return substr($haystack, -mb_strlen($needle)) === $needle;
    }

    function end2($haystack, $needle) {
        return strpos($haystack, $needle) === (mb_strlen($haystack) - mb_strlen($needle));
    }
    
    function end3($haystack, $needle) {
        return substr_compare($haystack, $needle, -mb_strlen($needle)) === 0;
    }