未定义的偏移量PHP,不确定它的作用

Question

有人可以帮忙,我在PHP error.log中有以下错误

[Tue Dec 19 12:08:22.887574 2017] [:error] [pid 32196] [client xx.xx.xx.x:20560] PHP注意:未定义的偏移量:/var/www/html/page.php中的8第55行,referer:view.php？1x = 8

和我认为导致这个问题的PHP代码是:

$i = isset($_SESSION['i']) ? $_SESSION['i'] : 0;
// echo $_SESSION['websites'][$i];
$website = explode(";", $_SESSION['websites'][$i]);
// echo $website[0];
$i++;
$_SESSION['i'] = $i;

我真的不知道是什么$i = isset($_SESSION['i']) ? $_SESSION['i'] : 0;做

谢谢

session_start();
$i = isset($_SESSION['i']) ? $_SESSION['i'] : 0;
if ($_SESSION['i'] < $sesioni1x) {  
    // echo $_SESSION['websites'][$i];
    $website = explode(";", $_SESSION['websites'][$i]);
    // echo $website[0];
    $i++;
    $_SESSION['i'] = $i;
        header("Location: $website[0]"); //redirect
        die();
        // echo $website[0];
        // echo $sesioni1x;
        // echo $website[0]." Frame-URL<br>";
        // $_SESSION['actual_website'] = $website[0];
}           
if ($_SESSION['i'] == $sesioni1x) {
    $handle = fopen($list1x, "a"); //open file to append content to csv file
    fputcsv($handle, $_SESSION['addwebsite'], ";"); //insert line in opened file
    fclose($handle); //close file
    header("Location: index.php"); //redirect
    die(); 
    // echo "session = var";
    }

这是我得到这个警告的完整代码,我必须说脚本正在完成他的工作,但我想摆脱错误

所述$_SESSION['i']源是0

Answer 1

这是三元运算符.基本上它是一个简单的if/else.

$i = (isset($_SESSION['i']) ? $_SESSION['i'] : 0);

为了帮助您理解它,这个代码在一行

if(isset($_SESSION['i'])){
    $i=$_SESSION['i'];
}
else{
    $i=0;
}