Variable multiplication not working as expected...

mmseng

Hi guys, it's been a while since I taught myself PHP, and I'm going back and noticing that I can't seem to get these variables to multiply like I want them.

Here's the code I'm working on:

    <?php

$daylength = 86400; //60*60*24

$current_date = time();

$days_ago = 0;
$secs_ago = $days_ago * $daylength;
$then_date = ($current_date - $secs_ago);
$filedate = date('Y-m-d', $then_date);
$filename = "file_$filedate.html";


// Testing variables
print "
\$daylength = $daylength<br />
\$current_date = $current_date <br />
\$days_ago = $days_ago <br />
\$secs_ago = $secs_ago <br />
\$then_date = $then_date <br />
\$filedate = $filedate <br />
\$filename = $filename <br />
<br />

";

print "

<h3>Here's a list of the daily files.</h3>

Today:<br />
<br />

";

if(file_exists($filename)) {
        print("<a href='./$filename'>$filedate</a><br />");
}

print "

<br />

Previous:<br />
<br />

";

for($days_ago = 1; $days_ago += 1; file_exists($filename)) {

// Testing variables
print "
\$daylength = $daylength<br />
\$current_date = $current_date <br />
\$days_ago = $days_ago <br />
\$secs_ago = $secs_ago <br />
\$then_date = $then_date <br />
\$filedate = $filedate <br />
\$filename = $filename <br />

";

        print("<a href='./$filename'>$filedate</a><br /><br />");
}

print "

<br />



";

?>

So the idea is that the loop increases $days_ago by 1 each time, and thus it is supposed to roll backwards printing a link to each previous file until there are no more previous files. But as proven by the variable tests, when $days_ago is incremented and I subsequently call $secs_ago (via $then_date via $filedate via $filename), $secs_ago always ends up as 0, thus making the loop infinitely print today's file link.

So can someone tell me why $secs_ago, when called, does not reflect its own calculation of $daylength * $days_ago? You can see what I mean in the current output below:

    $daylength = 86400
    $current_date = 1204030895
    $days_ago = 0
    $secs_ago = 0
    $then_date = 1204030895
    $filedate = 2008-02-26
    $filename = file_2008-02-26.html

Here's a list of the daily files.

Today:

2008-02-26

Previous:

$daylength = 86400
$current_date = 1204030895
$days_ago = 2
$secs_ago = 0
$then_date = 1204030895
$filedate = 2008-02-26
$filename = file_2008-02-26.html
2008-02-26

$daylength = 86400
$current_date = 1204030895
$days_ago = 3
$secs_ago = 0
$then_date = 1204030895
$filedate = 2008-02-26
$filename = file_2008-02-26.html
2008-02-26

$daylength = 86400
$current_date = 1204030895
$days_ago = 4
$secs_ago = 0
$then_date = 1204030895
$filedate = 2008-02-26
$filename = file_2008-02-26.html
2008-02-26

...
...
...

Thanks in advance,
== Matt

Plookie

The syntax for your "for" loop is a little off.

You have

for($days_ago = 1; $days_ago += 1; file_exists($filename)) {

which translates to

for(<start>; <increment>; <condition>)

It should be

for(<start>; <condition>; <increment>)

which would make your code

for($days_ago = 1; file_exists($filename); $days_ago += 1)

What is happening is that you are testing whether the operation "$days_ago += 1" returns true, or a positive value. Since the counter will always be a positive value (since you started at 1), the condition will always be true, which will result in an infinite loop.

Hope this helps,

Paul

mmseng

Aha. That was the biggest problem. Thanks. I also remembered that I'm supposed to be a programmer or something... and started acting like it. Here's what I ended up with, it works great.

<?php

$daylength = 86400; //60*60*24
$path = '/path/to/file/';
$name_prefix = 'file_';
$link_path = './files/';
$current_date = time();

print "
<h3>Here's a list of the daily files.</h3>

Today:<br />
<br />
";

if (report_exists_from_x_days_ago(0)) {

    $filename = report_name_from_x_days_ago(0);
    $filedate = report_date_from_x_days_ago(0);
    $link = $link_path . $filename;
    print("<a href='$link'>$filedate</a><br /><br />");
}

print "
Previous:<br />
<br />
";

for($days_ago = 1; report_exists_from_x_days_ago($days_ago); $days_ago += 1) {

    $filename = report_name_from_x_days_ago($days_ago);
    $filedate = report_date_from_x_days_ago($days_ago);
    $link = $link_path . $filename;
    print("<a href='$link'>$filedate</a><br /><br />");
}


function report_exists_from_x_days_ago($days_ago) {

    global $path;

    $filename = report_name_from_x_days_ago($days_ago);
    $filepath = $path . $filename;
    $exists = file_exists($filepath);

    return $exists;
}

function report_name_from_x_days_ago($days_ago) {

    global $name_prefix;

    $filedate = report_date_from_x_days_ago($days_ago);
    $filename = $name_prefix . $filedate . ".html";

    return $filename;
}

function report_date_from_x_days_ago($days_ago) {

    global $daylength;
    global $current_date;

    $secs_ago = $days_ago * $daylength;
    $then_date = ($current_date - $secs_ago);
    $filedate = date('Y-m-d', $then_date);

    return $filedate;
}

?>

Hooray for functions and well-used globals 😃 ... and of course proper for loop syntax :o

bradgrafelman

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