先发这么些,请大家在评论中继续添加

function GetIP() { //获取IP
    if ($_SERVER["HTTP_X_FORWARDED_FOR"])
        $ip = $_SERVER["HTTP_X_FORWARDED_FOR"];
    else if ($_SERVER["HTTP_CLIENT_IP"])
        $ip = $_SERVER["HTTP_CLIENT_IP"];
    else if ($_SERVER["REMOTE_ADDR"])
        $ip = $_SERVER["REMOTE_ADDR"];
    else if (getenv("HTTP_X_FORWARDED_FOR"))
        $ip = getenv("HTTP_X_FORWARDED_FOR");
    else if (getenv("HTTP_CLIENT_IP"))
        $ip = getenv("HTTP_CLIENT_IP");
    else if (getenv("REMOTE_ADDR"))
        $ip = getenv("REMOTE_ADDR");
    else
        $ip = "Unknown";
    return $ip;
}

function DateAdd($date, $int, $unit = "d") { //时间的增加（还可以改进成时分秒都可以增加，有时间再补上）
    $dateArr = explode("-", $date);
    $value[$unit] = $int;
    return date("Y-m-d", mktime(0,0,0, $dateArr[1] + $value['m'], $dateArr[2] + $value['d'], $dateArr[0] + $value['y']));
}

function GetWeekDay($date) {  //计算出给出的日期是星期几
    $dateArr = explode("-", $date);
    return date("w", mktime(0,0,0,$dateArr[1],$dateArr[2],$dateArr[0]));
}

function check_date($date) { //检查日期是否合法日期
    $dateArr = explode("-", $date);
    if (is_numeric($dateArr[0]) && is_numeric($dateArr[1]) && is_numeric($dateArr[2])) {
        return checkdate($dateArr[1],$dateArr[2],$dateArr[0]);
    }
    return false;
}
function check_time($time) {  //检查时间是否合法时间
    $timeArr = explode(":", $time);
    if (is_numeric($timeArr[0]) && is_numeric($timeArr[1]) && is_numeric($timeArr[2])) {
        if (($timeArr[0] >= 0 && $timeArr[0] <= 23) && ($timeArr[1] >= 0 && $timeArr[1] <= 59) && ($timeArr[2] >= 0 && $timeArr[2] <= 59))
            return true;
        else
            return false;
    }
    return false;
}

function DateDiff($date1, $date2, $unit = "") { //时间比较函数，返回两个日期相差几秒、几分钟、几小时或几天
    switch ($unit) {
        case 's':
            $dividend = 1;
            break;
        case 'i':
            $dividend = 60;
            break;
        case 'h':
            $dividend = 3600;
            break;
        case 'd':
            $dividend = 86400;
            break;
        default:
            $dividend = 86400;
    }
    $time1 = strtotime($date1);
    $time2 = strtotime($date2);
    if ($time1 && $time2)
        return (float)($time1 - $time2) / $dividend;
    return false;
}
function left($str, $len) {  //解决中文被截成乱码的问题  类似ASP的LEFT
    $arr = str_split($str);
    $i = 0;
    foreach ($arr as $chr) {
        if (ord($chr) > 128)
            $add = $add ? 0 : 1;
        $i++;
        if ($i == $len)
            break;
    }
    return substr($str, 0, $len + $add);
}

function get_querystring($not_in = "Submit") { //获取$_GET和$_POST中的各项，并返回字符串
    $querystring = "";
    $GET_POST = array_merge($_POST,$_GET);
    foreach($GET_POST as $key=>$value) {
        if ($value=="" || preg_match("/$not_in/i",$key))
            continue;
        $querystring .= "$key=$value&";
    }
    if ($querystring)
        return substr($querystring,0,-1);
    return "";
}

function get_innerhtml($html,$label) {   //获取一对html标记间的html字符串
    $result_arr = preg_split("/<\/".$label.">/i",$html);
    $pattern = "/<".$label.".*?>/i";
    for ($i = 0; $i < count($result_arr); $i++) {
        list($left, $right) = preg_split($pattern,$result_arr[$i],2);
        $result_arr[$i] = $right;
    }
    return $result_arr;
}
//例: echo get_innerhtml("<tr><td height=20>something</td></tr>", "td");   //will print "something".

function get_input_value($input) { //获取Input的HTML代码中的Value值
    $pos = stripos($input, "value=") + 6;
    if ($pos !== false) {
        $input = substr($input, $pos);
        if (substr($input, 0, 1) == "\"")
            return substr($input, 1, strpos($input, "\"", 1) - 1);
        else
            return substr($input, 0, strpos($input, " ") - 1);
    }
    return false;
}

function getcontentbetween($a, $b, $str) { //获取字符串$str中,字符串$a与字符串$b之间的字符串
    if ($str!=="" && $a!=="" && $b!=="") {
        $start = strpos($str, $a) + strlen($a);
        return substr($str, $start, strpos($str, $b, $start + 1) - $start);
    }
    return false;
}