Variable multiplication not working as expected...

[msing]

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 />

";

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 />

";

$days_ago = 1;
while(file_exists($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 />");
        $days_ago += 1;
}

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. 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), $sec_ago always ends up as 0, thus making the loop at the end 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?

 

Thanks in advance,

== Matt

[fnairb]

I got burned by this one just the other day.  It is the whole daylight savings time garbage.

 

Try:

// Create a date object for now

$dt = date_create();

// Use a negative -1 for yesterday, -2 for two days ago, etc

date_modify($dt, $days_ago . ' days');

$filedate = date('Y-m-d', $then_date);

$filename = "file_$filedate.html";

 

 

If you are doing some sort of looping remember that each time you update $dt would be cumulative sorta....

 

<?php

// Create a date object for now

$dt = date_create();

 

// Probably wrong:  today, yesterday, 3 days ago, 6 days ago...

for ($i = 0; $i < 5; $i++) {

  date_modify($dt, '-' . $i . ' days');

  echo $dt->format('Y-m-d'), "\n";

}

 

$dt = date_create();

 

// Probably correct:  today, yesterday, 2 days ago, 3 days ago...

for ($i = 0; $i < 5; $i++) {

  date_modify($dt, '-1 days');

  echo $dt->format('Y-m-d'), "\n";

}

?>

 

[sasa]

you must recalculate your variables in loop

[msing]

@fnairb: I might give that a try, but I'm really more concerned with why my current code doesn't work. I don't see how daylight savings time has anything to do with this. It looks to me like a simple calculation error.

 

For some reason $secs_ago (a.k.a. $days_ago * $daylength) always = 0, no matter what those values are.

 

you must recalculate your variables in loop

 

Ok, but how and why?

[sasa]

while(file_exists($filename)) {
//recalculte
$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 />

";

        print("<a href='./$filename'>$filedate</a><br />");
        $days_ago += 1;
}

[msing]

Ah yes, it's all starting to come back to me now. I really wish I could just use a function to re-run the values on these variables every time I wanted the values for a different number of days ago. But as I recall using globals in conjunction with functions is a nightmare. Too bad it can't just be like Perl, where you can turn globals on and off per file.

 

Anyway, here is what I have now. It seems to be working for the most part. The first two file_exists test works, but the file_exists test in the for loop don't seem to return a bool like they're supposed to. See anything wrong?

 

<?php

$daylength = 86400; //60*60*24
$path = '/path/to/file/';
$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";
$filepath = $path . $filename;
$exists = file_exists($filepath);

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

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

// Testing variables
print "
\$daylength = $daylength<br />
\$path = $path<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 />
\$filepath = $filepath<br />
\$exists = $exists<br />
";

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

print "
<br />

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

for($i = 0; $i += 1; file_exists($filepath)) {

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

        // 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 />
        \$filepath = $filepath <br />
        \$exists = $exists <br />
        ";

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

?>

 

So the output is still looping:

 

Here's a list of the daily files.

Today:

 

$daylength = 86400

$path = /path/to/file/

$current_date = 1204065178

$days_ago = 0

$secs_ago = 0

$then_date = 1204065178

$filedate = 2008-02-26

$filename = file_2008-02-26.html

$filepath = /path/to/file/file_2008-02-26.html

$exists = 1

2008-02-26

 

Previous:

 

$daylength = 86400

$current_date = 1204065178

$days_ago = 1

$secs_ago = 86400

$then_date = 1203978778

$filedate = 2008-02-25

$filename = file_2008-02-25.html

$filepath = /path/to/file/file_2008-02-25.html

$exists =

2008-02-25

 

$daylength = 86400

$current_date = 1204065178

$days_ago = 2

$secs_ago = 172800

$then_date = 1203892378

$filedate = 2008-02-24

$filename = file_2008-02-24.html

$filepath = /path/to/file/file_2008-02-24.html

$exists =

2008-02-24

 

$daylength = 86400

$current_date = 1204065178

$days_ago = 3

$secs_ago = 259200

$then_date = 1203805978

$filedate = 2008-02-23

$filename = file_2008-02-23.html

$filepath = /path/to/file/file_2008-02-23.html

$exists =

2008-02-23

[msing]

Ok, I got it now. The loop syntax 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

[revraz]

Was wondering when you would figure out that 0 * anything is still 0

 

$days_ago = 0;

$secs_ago = $days_ago * $daylength;