【求助】为什么setcookie函数总是返回false

购物车功能。我建了一个过渡页面，用于存储cookies和跳转，也避免setcookie函数和网页标签在一个页面中，容易有冲突。可是！setcookie函数始终返回false!我不知道到底哪里写错了啊！
求教了啊啊啊啊！阿里嘎多妥妥的！！！！
以下是页面源码
<?php
$newP = 5;
$select = 3;
if($newP != '0') {
if(!isset($_COOKIE["cartC"])) {
$cart = array();
}
if(array_key_exists("$newP", $cart)) {
$cart["$newP"] += $amount;
$cart_arr = serialize($cart);
$test = setcookie("cartC", $cart_arr, time()+3600);
} else {
$cart["$newP"] = $amount;
$cart_arr = serialize($cart);
$test = setcookie("cartC", $cart_arr);
}
if($test == true) {
echo "<script language=javascript>window.location.href='memberarea5.php';</script>";
} else {
echo "errors exist when the setcookie executed";
}
}
?>