Theo’s Blog

Last night I ran into the crazy problem that a mysql result set contained rows (confirmed with mysql_num_rows) but I wasn’t able to fetch the rows in mysql_fetch_array while loop construction. I managed to create a workaround but I posted a note on the php.net mysql_fetch_array page asking for an explanation. The note got rejected so I figured I could use my own blog in the search for an answer.

Here is the note;

I hope someone can help me with this question.

I have 2 code snippets. The first works, the second doesn’t. I would prefer using the second code snippet because it seems cleaner. What’s wrong with the second code snippet?

This works;

$results = mysql_query("SELECT DISTINCT(col) FROM table WHERE col!='' ORDER BY RAND()");
for( $i = 0; $i < mysql_num_rows( $results ); $i++ )
{
// do something with mysql_result($results,$i,0);
}

This doesn’t work;

$results = mysql_query("SELECT DISTINCT(col) FROM table WHERE col!='' ORDER BY RAND()");

 while($result = mysql_fetch_array($results))
 {
 //do something with $result
 }

I’m writing a web application that allows it’s users (among other things) to upload their company logos. PHP script is used to take the user provided jpgs/pngs and present them uniformly in a webpage. I ran into the problem that rescaled png images had their transparent regions turned black.

Here’s the solution I found;

• First create a new image (imagecreatetruecolor) with the required dimensions.
• Allocate a transparent color for that image. (imagecolorallocatealpha)
• Fill the image with the transparent color. (imagefilledrectangle)
• Now copy a scaled version of your original png image into the new image. (imagecopyresampled)

Voila.

Although the last step effectively overwrites all the pixels in your image, step 2 and 3 seem to be absolutely necessary to allow transparency inside your png image.

One more word of advice; use imagecopyresampled instead of imagecopyresized.

Resampled

Resampled "Dutch Design Award"

Resized

Resized "Dutch Design Award"

I encountered a problem with displaying a “loader” (a progress-bar) for downloading a dynamically generated XML. The loader would remain 0% until the XML was completely loaded. The problem is that the web server providing the XML didn’t send file-size information in it’s HTTP headers, as it doesn’t know file-size prior to generating the XML. Here is a trick that you can use when using PHP code on the server-side to wait for the XML generation process to finish before serving the client, so that the file-size can be put in the HTTP headers.

ob_start()

ob_start(‘ob_gzhandler’);

… output the XML content…

ob_end_flush();

header(‘Content-Length: ‘.ob_get_length());

header(“Content-Type: text/xml”);

ob_end_flush();