CODEWITHSUNDEEP
phprandom
JamesBriggs
JamesBriggs

Reputation: 137

PHP random link without repetitions

My PHP is poor, but I'm trying my best to improve!!

I'm attempting to code a really simple php script that loads a random html page from a text file list.

Once people have viewed the html page, they link back to the random.php file and it loads another page... this can continue on forever.

I'm using a text file list as I'll regularly be adding more pages. My issue is there is no where in my code to prevent repeat visits!! Right now I only have about 8 links, and on more than one occasion I've had the same link 'randomly' come up 3 times in a row :( Hoping there is something simple I can add to this to prevent repetitions, and if all links have been viewed, then it resets. Many Thanks :) 

    <body>

    <?php
    $urlist=file("randomlinks.txt");
    $nl=count($urlist);
    $np=rand(0,$nl-1);
    $url=trim($urlist[$np]);
    header("Location: $url");
    exit;
    ?>

    </body>

Upvotes: 2

Views: 1053

Answers (3)

Travesty3
Travesty3

Reputation: 14479

I would use PHP sessions to do this. Take a look at this example.

Store an array of available pages in a session variable. Every time you get a page, you remove that page from the array. When the array is empty, you reset it again from your original source.

Here's what your code might look like:

session_start();
if (empty($_SESSION["pages"]))
    $_SESSION["pages"] = file("randomlinks.txt");

$nl = count($_SESSION["pages"]);
$np = mt_rand(0, $nl-1);

// get the page, remove it from the array, and shift all higher elements down:
list($url) = array_splice($_SESSION["pages"], $page, 1);

die(header("Location: $url"));

Upvotes: 1

LSerni
LSerni

Reputation: 57408

Since the user does not know in what order the links are in the text file, if you were to read said links in sequence they would seem "random" (and you can shuffle them when first creating the file).

So you can:

  • save in session the index of the last link seen
  • link the link index to system time. This does not prevent repetitions, but guarantees that no two links come out equal, unless you hit 'refresh' after exactly the right amount of time.

Method 1:

$urlist=file("randomlinks.txt");
$nl=count($urlist);

session_start();
if (!isset($_SESSION['link'])) // If link is not in session
    $_SESSION['link'] = 0;    // Start from 0 (the first)
$np = $_SESSION['link']++;    // Next time will use next
$_SESSION['link'] %= $nl;     // Start over if nl exceeded

$url=trim($urlist[$np]);
Header("Location: $url");

Method 2:

...
$nl=count($urlist);
$np = time() % $nl;           // Get number of seconds since the Epoch,
                              // extract modulo $nl obtaining a number that
                              // cycles between 0 and $nl-1, every $nl seconds
$url=trim($urlist[$np]);
Header("Location: $url");

Another method would be to remember the last N links seen - but for this, you need a session variable - so as not to get them again too soon.

session_start();
if (!isset($_SESSION['urlist']))       // Do we know the user?
    $_SESSION['urlist'] = array();     // No, start with empty list
if (empty($_SESSION['urlist']))        // Is the list empty?
{
    $_SESSION['urlist'] = file("randomlinks.txt");   // Fill it.
    $safe = array_pop($_SESSION['urlist']);
    shuffle($_SESSION['urlist']);           // Shuffle the list
    array_push($_SESSION['urlist'], $safe);
}
$url = trim(array_pop($_SESSION['urlist']));

If you have five URLS 1, 2, 3, 4 and 5, you might get:

1 5 3 4 2 1 4 2 5 3 1 2 3 5 4 1 4 3 2 5 1 4 ...

...the list is N-1 random :-), all links appear with equal frequency, and the same link may reappear at most at a 2-remove, like the "4" above (...4 1 4...); if it does, you'll never see it again for at least $nl visits.

ALSO

  1. You should not use Header() from within a <BODY> tag. Remove <BODY> altogether.
  2. You don't need to use exit() if you are at the natural end of the script: the script will exit by itself.

Upvotes: 2

Tsubashi
Tsubashi

Reputation: 740

The simplest way I can think of would be to use a cookie.

The Internet is full of tutorials such as the following: http://www.w3schools.com/php/php_cookies.asp

For example:

<?php
if (isset($_COOKIE["vistList"]))
  $visited = split(","$_COOKIE["visitList"]);
  foreach ($visited as &$value) {
    if ($value == /* new site url */) {
      //Find a new one
    }
  }
else
  $expire=time()+60*60*24*30;
  setcookie("vistList", "List-of-visited-URLs, separated-by-commas", $expire);
?>

I have not had a chance to test this code, but hopefully it can give you ideas.

As noted in the comments, the same thing could be accomplished using php sessions:

<?php
session_start();
if (isset($_SESSION["vistList"]))
  $visited = split(","$_SESSION["visitList"]);
  foreach ($visited as &$value) {
    if ($value == /* new site url */) {
      //Find a new one
    }
  }
else
  $_SESSION['vistList']=/* new site URL */
?>

Upvotes: 1

Related Questions