PHP: more efficient (if else vs switch)

Zeno McDohl · 12-16-2008, 03:28 PM

I have PHP code (rather hackish) to tie together an ad manager and Joomla. It's a bunch of if else's right now and it's obviously inefficient. I'm also starting to get PHP "memory exhausted" errors. If I changed these all to a switch statement, would it help much? Or any suggestions what I should do instead?

The code is something like this:

Code:

if(strstr($_SERVER['REQUEST_URI'], "catid=2569&"))
{
echo '<script type="text/javascript" language="javascript" src="components/com_ijoomla_ad_agency/ijoomla_ad_agency_zone.php?zid=461"></script>';
}//endif for strstr 2569
else if(strstr($_SERVER['REQUEST_URI'], "catid=2570&"))
{
echo '<script type="text/javascript" language="javascript" src="components/com_ijoomla_ad_agency/ijoomla_ad_agency_zone.php?zid=462"></script>';
}//endif for strstr 2570

titanium_geek · 12-16-2008, 05:20 PM

*I am not a php guru

You are calling request_uri multiple times- would it be better to pull that in as a static variable for the purposes of this bit of code and then use it over and over again? (again, I am not an efficiency guru.) That way you wouldn't have
"what's the uri? uhh... go. what's the uri? uhh... go." but "what's the uri? this is. go! go! go!"

A point of clarification:
You've got two if/else statements here- that seems pretty reasonable, but do you actually have scads (lots) of the things?

I seem to remember from uni that switches aren't actually much better memory wise than if else statements, but that was java, that was 2 years ago, and there might be some "user brain memory error" there.

From: Clean and Efficient Coding Technique in PHP

Quote:

Case Statements - A case statement produces roughly 1/5th the amount of machine code as an if/else structure that completes the same task. Use case statements whenever possible. The difference in memory overhead between these two statements is fairly nominal, but the case statement is more efficient to some small degree.

Also: http://rob.sun3.org/php-code/switch-vs-if/

TG

graemef · 12-16-2008, 05:26 PM

Given that you have it structured as an if else, I cannot imagine that there would be any significant performance difference changing it to a switch. A switch does make it easier to read but that is about all. I would expect that your "memory exhausted" errors are coming from something else and that would be worth investigating do various checks with memory_get_peak_usage() and memory_get_usage() at the start and end of the functions that you suspect to be problematic.

graemef · 12-16-2008, 05:53 PM

Looking at the code a little more, maybe the repeated use of strstr() in the if statement is a problem (particularly if there are lots of them. You can use preg_grep() to return the matches of a pattern of the URI and then do a switch/ if else on that.

Zeno McDohl · 12-17-2008, 12:07 PM

[17-Dec-2008 12:45:54] PHP Fatal error: Call to undefined function: memory_get_usage()

Took out all the checks on URI by storing it in a var. Still getting memory exhausted.

How would I use preg_grep on a string? Doesn't seem easy to find examples and everything deals with arrays.

Oh and there are plenty more ifchecks in the same format. Wasn't going to paste everything.

jiml8 · 12-17-2008, 12:22 PM

Back to basics. Why do you think the memory error is coming about in this segment of code anyway?

If it were me, I would parse the catid=number string to pull out the number, then use that as an index into a database to pull up the desired zid=. It would lead to a much smaller script and would be far, far easier to maintain.

Zeno McDohl · 12-17-2008, 12:24 PM

Because this entire file (ads.php) is full of just these ifchecks. And if I uncomment them all, I get this:
[17-Dec-2008 12:57:01] PHP Parse error: memory exhausted in /home/user/public_html/ads.php on line 5552

I have to comment out the ifchecks from line 5552 and on in order for the code to work.

jiml8 · 12-17-2008, 12:30 PM

Well, then, I'm guessing that the if statements are creating temp variables that don't go away until the last if statement in the chain.

If you are doing this thousands of times, then you certainly need to find a better way. Use a database, or use indirection and loop over the if statement, filling in the test value each time. Something other than the brute force method you are using.

Zeno McDohl · 12-17-2008, 12:38 PM

A database was the final step, just wanted to get a quick fix done today.

Thanks though, gonna work on the db.

And shouldn't I be using preg_match, not preg_grep? Regardless, trying to think up a regex that would get the ID from the URI.

jiml8 · 12-17-2008, 01:27 PM

Seems to me that putting a database in immediately is a quicker fix than writing out thousands of else if statements.

Zeno McDohl · 12-17-2008, 01:30 PM

All I would have needed to do was write one if statement in Excel and double clicked.

I have the data in Excel, so using cell refs it would be very quick.

jiml8 · 12-17-2008, 01:36 PM

based on the sample code given:

Code:

$ii = 1;
while ($ii < 2000)
{
    $tmp_catid = $ii + 2108;
    $tmp_catid = "catid=".$tmp_catid;
    if(strstr($_SERVER['REQUEST_URI'], $tmp_catid))
    {
        echo '<script type="text/javascript" language="javascript" src="components/com_ijoomla_ad_agency/ijoomla_ad_agency_zone.php?zid='.$ii.'"></script>';
        $ii = 2000;
    } else {
        $ii = $ii+1;
    }
}

This picks up everything in just a handful of lines.

graemef · 12-17-2008, 05:18 PM

First, getting the catid from the URI, this should be available from the $_GET super variable $_GET['catid']
Second, if you are just performing a lookup from the catid to a zid then a database makes some sense, other alternatives would be to store all the possibilities in an array, record it in a file, but given that you appear to have thousands of them the database would be the most flexible. However, the quick solution would be the array.

PHP Code:



lookup = array {2569 => 461 
               ,2570 =>462 
               ,2571 =>463 
               } 
echo '<script type="text/javascript" language="javascript" src="components/com_ijoomla_ad_agency/ijoomla_ad_agency_zone.php?zid='.lookup[$_GET['catid']].'"></script>';

You will want to wrap some code around this: check that the catid exists, check that the catid key exists in the lookup array. If the code uses values other than 'catid' from the URI then the code will need to take this into account

Finally, the memory_get_usage() function is available as part of PHP for version 4.3.2 or later, so are you using an older version? If so you may want to consider upgrading the version.