PHP截取含中文的混合字符串长度的函数

截取含中文的混合字符串长度

    /**
     * 截取中文混合字符串指定长度
     * 
     * @param string $string
     * @param integer $length
     * @param string $etc 超过长度时的省略符
     * @param string $charset 字符编码 utf-8 或者 gbk
     * @return string
     */
    public function truncateCn($string, $length = 80, $etc = '...', $charset = 'utf-8')
    {
        if ($length == 0) {
            return '';
        }
           
        if (function_exists('mb_substr')) {
            $etc = mb_strlen($string, $charset) > $length ? $etc : '';
            return mb_substr($string, 0, $length, $charset) . $etc;
        }
           
        if ($charset == 'utf-8') {
            $pa = "/[x01-x7f]|[xc2-xdf][x80-xbf]|xe0[xa0-xbf][x80-xbf]|[xe1-xef][x80-xbf][x80-xbf]|xf0[x90-xbf][x80-xbf][x80-xbf]|[xf1-xf7][x80-xbf][x80-xbf][x80-xbf]/";
        }
        else {
            $pa = "/[x01-x7f]|[xa1-xff][xa1-xff]/";
        }
        preg_match_all($pa, $string, $t_string);
        if (count($t_string[0]) > $length) {
            return join('', array_slice($t_string[0], 0, $length)) . $etc;
        }
           
        return join('', array_slice($t_string[0], 0, $length));
    }