<?php /*定义和用法substr() 函数返回提取的子字符串, 或者在失败时返回 FALSE。 语法substr(string,start,length)参数 描述string 必需。规定要返回其中一部分的字符串。start 必需。规定在字符串的何处开始。非负数 - 从 string 的 start 位置开始,从 0 开始计算.负数 - 从 string 结尾处向前数第 start 个字符开始。 如果 string 的长度小于或等于 start,将返回 FALSE。 length 可选。规定要返回的字符串长度。默认是直到字符串的结尾。正数 - 从 start 处开始最多包括 length 个字符(取决于 string 的长度)。 负数 - 去除从string 结尾处向前length个字符如果提供了值为 0,FALSE 或 NULL 的 length,那么将返回一个空字符串。 */$str = "abcdefghijklmn";$rest = substr($str, 0); // 返回 "abcdefghijklmn"echo $rest . "<br/>";$rest = substr($str, 1, 3); // 返回 "bcd"echo $rest . "<br>";$rest = substr($str, -3); // 返回 "lmn"echo $rest . "<br>";$rest = substr($str, -3, 2); // 返回 "lm"echo $rest . "<br>";$rest = substr($str, 1, -3); // 返回 "bcdefghijk"echo $rest . "<br>";$rest = substr($str, -7, -3); // 返回 "hijk"echo $rest . "<br>";?>

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