PHP

The singleton design pattern is used to centralise an object in an application that is used to store changing variables that can then be accessed by other parts of the program. It allows only the single instantiation of an object, hence the name.

The main use of a singleton is to create an alternative to the use of global variables. Although global variables are useful they can lead to a major problem if you happen to assign two variables with the same name, PHP generates no errors and your program will start to act oddly. This might not be a problem in small programs, but in larger systems it is very easy to have global variable clashes.

The singleton pattern gets around this by using an single object that is accessible to any part of the program that wants it. If two classes are declared with the same name PHP throws an error so if another part of the program tries to use the same class name you will know about it.

Every time you accept any input from a use you should attempt to validate it. This is to stop users trying to break the site and also corrects silly mistakes that users might introduce to their input.

Before sending off an email to a new user congratulating them on signing up it is best to validate that email address. Here is function that does this.

function validateEmail($email)
{
  $reg_exp = '/^[A-z0-9][\w.-]*@[A-z0-9][\w\-\.]+\.[A-z0-9]{2,3}$/';
  if (preg_match($reg_exp, $email) == true) {
    return true;
  } else {
    return false;
  }
}

This can be used in the following way.

The Exif/IFD0 functions in PHP work with images to pull out meta data associated with them. Most image applications and digital cameras will produce an image with a certain amount of meta data present. This is obvious stuff like file size and creation time stamps, but you can also get stuff like copy right notices, camera name, date picture taken and even things like location if the camera was linked to a GPS system. This meta data can be used to sort or categorise images.

Installation

On Linux systems you must configure exif support with the command --enable-exif when calling the configure script.

On Windows all you have to do is uncomment the lines in your php.ini file for the DLL's php_exif.dll and php_mbstring.dll. However, you must ensure that the php_mbstring.dll DLL is loaded before the php_exif.dll DLL. So you will need to edit your php.ini file so that php_mbstring.dll is located above php_exif.dll.

To detect a user returning to a web page you can use the built in PHP session manager. At the start of the code you can use the session_start() function to initiate the session, you can then use the $_SESSION global array to store and retrieve information. The session_start() function sends a cookie to the client with a unique code that looks like this

8a9af5644326881594811db6fe96faf8

The session variable information is kept in a file on the web server and when the session_start() function is called PHP looks for the file with the corresponding name. It then parses this file and loads the variables into memory. This is all done behind the scenes by PHP, all you need to know is that you can set values in the $_SESSION array and get them back the next time the page is loaded.

Sometimes is is necessary to see how long your PHP code runs for. This can be done using the following function and examples. This will convert the result of the php function microtime() into a float value.

function getmicrotime($t){
  list($usec, $sec) = explode(" ",$t);
  return ((float)$usec + (float)$sec);  
}

Use this function to see how long something runs for. At the start of the code call the microtime() function and store the result at the start. At the end store the result of the microtime() function as the end and then use the two values to figure out how long the code took to run.

Generating CSS with PHP has several benefits. For example, you can keep all of your colour declarations as PHP variables so if you need to change any colours it only takes a small edit and not a find/replace operation.

Getting PHP to generate CSS requires just two steps. The first thing to do is to open your CSS file and insert the following line at the top. This tells the browser that the file is CSS.

PHP has some very nice error reporting features, which can tell you many things about the code that you are trying to execute. This error reporting is always nice to have available when debugging code as it helps you solve many of the common mistakes that occur when creating dynamic web pages.

However, this error reporting is almost always turned off on production servers as it can reveal information about the server that you wouldn’t want everyone to see. For example, the errors can reveal information about server file structure, database fields in queries, database usernames, $_GET and $_POST commands and so on.

To randomise an array in PHP use the shuffle() function like this.

$array = range(1, 5);
shuffle($array); // randomise array

There are two limitations to this function. The first is that it completely removes any key association that you may have set up. So the following array.

$array = array('one'=>1,'two'=>2);

Would be turned into the following after using shuffle().

Array
(
  [0] => 2
  [1] => 1
)

A way around this is to use the following function, this uses the PHP function array_rand() to extract the all of the keys in the array in a random order before ensuring that the key associations are in place.

It is widely known that the data that Alexa offers on visitor numbers is far from accurate, but it is possible to obtain an XML feed from Alexa that allows you to find out all of the data that Alexa offers, which is more than just their visitor numbers. Passing the correct parameters to this feed you can find out related links, contact and domain information, the Alexa rank, associated keywords and Dmoz listings.

As an example here is a feed URL for getting information about the bbc.co.uk page.

http://xml.alexa.com/data?cli=10&dat=nsa&ver=quirk-searchstatus&uid=19700101000000&userip=127.0.0.1&url=www.bbc.co.uk

So to get information about any site all you have to do is pass the correct URL to this address.

To get this information in a usable form with PHP you can use the curl functions. To download the Alexa feed into PHP use the following code:

The str_word_count() function in PHP does exactly what is says it does. The default of this function is to simply count the number of words present. Take the following string.

$str = "This is a 'string' containing m0re than one word. This is a 'string' containing m0re than one word.";

If we pass this to the str_word_count() function with no other parameters we get the number of words.

echo str_word_count($str); // prints 20

The second parameter is the type of value returned from the function. The default value is 0, but 1 and 2 are also available. Using 1 as the second parameters returns an array containing all the words found inside the string. Using 2 returns an associative array, where the key is the numeric position of the word inside the string and the value is the actual word itself. Here are the results from setting the second parameter to 1.