What is this code and this operator?

[+ 0.5]

Hi All,

Found this code and it does exactly what I want, but I need to execute multiple times on the same page. The idea is to have a group of image files in a directory and use this code to randomly display one. Since I use it up to three times on the same page and it appears to use the time as the seed for the calculation, without modification it shows the same image 3 times.

I added something and it is working now, but would like to understand it better. My solution was to change a line of code and save the file with a new name. I have 3 files and vary which one is called.

Here's the file:

<?php

    $folder = '.';

    $extList = array();
    $extList['gif'] = 'image/gif';
    $extList['jpg'] = 'image/jpeg';
    $extList['jpeg'] = 'image/jpeg';
    $extList['png'] = 'image/png';

$img = null;

if (substr($folder,-1) != '/') {
    $folder = $folder.'/';
}

if (isset($_GET['img'])) {
    $imageInfo = pathinfo($_GET['img']);
    if (
        isset( $extList[ strtolower( $imageInfo['extension'] ) ] ) &&
        file_exists( $folder.$imageInfo['basename'] )
) {
    $img = $folder.$imageInfo['basename'];
}
} else {
    $fileList = array();
    $handle = opendir($folder);
    while ( false !== ( $file = readdir($handle) ) ) {
        $file_info = pathinfo($file);
        if (
            isset( $extList[ strtolower( $file_info['extension'] ) ] )
) {
            $fileList[] = $file;
        }
    }
    closedir($handle);

    if (count($fileList) > 0) {
        $imageNumber = time() % count($fileList);
        $img = $folder.$fileList[$imageNumber];
    }
}
if ($img!=null) {
    $imageInfo = pathinfo($img);
    $contentType = 'Content-type: '.$extList[ $imageInfo['extension'] ];
    header ($contentType);
    readfile($img);
} else {
    if ( function_exists('imagecreate') ) {
        header ("Content-type: image/png");
        $im = @imagecreate (100, 100)
            or die ("Cannot initialize new GD image stream");
        $background_color = imagecolorallocate ($im, 255, 255, 255);
        $text_color = imagecolorallocate ($im, 0,0,0);
        imagestring ($im, 2, 5, 5, "IMAGE ERROR", $text_color);
        imagepng ($im);
        imagedestroy($im);
    }
}
?>

I modifiied this line:

$imageNumber = time() % count($fileList) + 0.5;

using 0.5 for one file and 1 for another. When I tried 2 it didn't work - which makes me think this sets $imageNumber to a decimal less than 1 but more than 0?

My question is what does the % operator do?

If I understood this code better, maybe there would be a way to only need one file instead of 3.

Thanks.

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Code:

$imageNumber = time() % count($fileList);

check this from the php manual:
http://nl2.php.net/manual/en/language.operators.arithmetic.php

EDIT: the code looks like some random image/banner generator...

Thanks for the link. That seems vaguely familiar from another language I've worked with.

Any idea on how to modify the script so I don't need 3 different copies to generate 3 different images on the same page?

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Any idea on how to modify the script so I don't need 3 different copies to generate 3 different images on the same page?

as I can see this script is written to use with different images:
this variable must holder the image name: $_GET['img']

here's some code I'm using to display random images:

Code:

<?php 
$DIRNAME = "./images/randoms/";   // Directory that contains the images

function DisplayRandomImage() 
{
global $DIRNAME;
$msg = ""; // IMG tag to be returned
$y = 0; // counter for the images
$images = array();       // array to hold the list of images to display randomly
$file_handle = "";


if (is_dir($DIRNAME)) 
{
$file_handle=opendir($DIRNAME); 
$y = 0;
while ($file = readdir($file_handle))  // while there's files to read....
{ 
     if (!is_dir($DIRNAME . $file)) 
{
  $pieces = explode (".", $file);
if ($pieces[0] && $pieces[1])  // filename.ext
{
if (($pieces[1]=="gif"))  // add only .gif files
{
     $images[$y] = $DIRNAME . $file; 
     $y += 1;
}
}
}
}
closedir($file_handle); 
if (count($images) > 0) 
{
         srand((double)microtime()*1000000);
$y = rand(0,(count($images) - 1));
$msg = "<IMG SRC=\"" . $images[$y] . "\" width=\"30\" height=\"80\" alt=\"\">";
} 
else 
{
$msg = "No image found in \"" . $DIRNAME . "\"\n";
}
} 
else 
{
$msg = "\"" . $DIRNAME . "\" is not a valid directory!\n";
}
return $msg;
} 
?>

This code is in the top of my page, after that HTML is used to create the page and where I want to display a random image I use

Code:

<?=DisplayRandomImage();?>

Does that code require building a file list? Many of the others I looked at do.

I can call the routine I use multiple times, unfortunately it is displaying the same image - I would guess the time only changes by seconds and therefore the resulting value is the same.

Do you use this with more than one image on the page?

Code:

$DIRNAME = "./images/randoms/";

refers to the directory the script looks at (in this case mydomain.com/images/randoms/) The scrip retrieves all the .gif images and displays a random one. If you have other images besides .gif you can change:

Code:

if (($pieces[1]=="gif"))

to:

Code:

if (($pieces[1]=="gif") OR ($pieces[1]=="jpg"))

for instance...
hope this helps!

edit: yes I use it with more then one image here: http://www.letsworkonline.com/ (its for the 2 images on the left next to the google ads) it can sometimes display the same image twice, but I guess that chance lowers when you add more images to your random image folder...

Thank you, I'll have to play with that some.

I noticed when testing that the incidence of the same image coming up goes down as the number of images in the directory goes up.

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I like Mind_nl's snippet, it can do what you want, and actually it can be optimized a little.

If you are about to have only the images in the $DIRNAME directory then you can replace this :

Code:

<?php
$pieces = explode (".", $file);
if ($pieces[0] && $pieces[1])  // filename.ext
{
if (($pieces[1]=="gif"))  // add only .gif files
{
      $images[$y] = $DIRNAME . $file; 
     $y += 1;
}
}

with this :

Code:

<?php
if ( is_file ( $file ) )
{
      $images[$y] = $DIRNAME . $file; 
     $y += 1;
}

This way it will work with any type of file too

Cool mod Nik, in my case the images are in a directory by themself.

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I just took a closer look and realized that this script is showing one random image.

You want one for as many as you want right?

No I think this is exactly what he wants (from what I read in the first post) one random image displayed, but the script called more then one time so he gets random images in different places on his page, thats just how I use this snippet

Code:

<?=DisplayRandomImage();?>

in different places in my HTML

edit: I like your optimization, but I often keep my photoshop files in the same directory (on my PC) and they sometimes get uploaded to the site too, I don't think displaying a .PSD file will work this way, so I'll leave in the part you optimized out 

[he]

No I think this is exactly what he wants (from what I read in the first post) one random image displayed, but the script called more then one time so he gets random images in different places on his page, thats just how I use this snippet

Code:

<?=DisplayRandomImage();?>

in different places in my HTML

Correct, except than the he

BTW I think this is a nice idea for the code gallery. I will make a snippet for random images tomorrow and post it there

The only bad thing about this snippet is that when you use it for more than one images, it can show the same image twice or more times....

But I will fix that

Yes, like I said before: it sometimes shows the same image more than once. I'd be very interested if you can fix that!

<Spoken in her deepest manliest voice...  >

Yes, Nik, I would love it if you could fix that too.

So, glad I came here and asked about this. 

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Ok, I will mark this thread as unread, and later on I will post you the code fragment you need

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Ok the snippet is done, with some extra feautures

http://www.webdigity.com/index.php?action=tutorial;code=32

Good work Nick! I'll be replacing my current random image script with this version.
One thing though: the code for displaying one random image is the same as for displaying more then one, looks like the second code line is missing something. Should that be:

Code:

<?php 
     echo RandomImage(3);

to display 3 random images?

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lol, that happens when you copy/paste

I have fixed that...

Nice job Nik.

I do have a couple of questions.

I would use the code multiple times in the same page, but not with t