Tag Archives: tutorial

PHP: Don’t Call the Destructor Explicitly

“PHP 5 introduces a destructor concept similar to that of other object-oriented languages, such as C++”[1] says the documentation for destructors, but let’s see the following class.

class A
	public function __construct()
		echo 'building an object';
	public function __destruct()
		echo 'destroying the object';
$obj = new A();

Well, as you can not call the constructor explicitly:


So we should not call the destructor explicitly:


The problem is that I’ve seen this many times, but it’s a pity that this won’t destroy the object and it is still a valid PHP code.
Continue reading PHP: Don’t Call the Destructor Explicitly

How to Check if a Date is More or Less Than a Month Ago with PHP

Let’s say we have the following problem: we have to check whether a date is more than a month ago or less than a month ago. Many developers go in the wrong direction by calculating the current month and then subtracting the number of months from it. Of course, this approach is slow and full of risks of allowing bugs. Since, two months before January, which is the first month of the year, is actually November, which is the eleventh month. Because of these pitfalls, this approach is entirely wrong.

strtotime() is a lot more powerful than you think!
strtotime() is a lot more powerful than you think!

The question is whether PHP cannot help us with built-in functions to perform these calculations for us. It is obvious, that from version 5.3.0 and later, there is an OOP section, which is great, but unfortunately this version is still not updated everywhere. So, how to accomplish the task?

The Wrong Approach

As I said, there are many ways to go in the wrong direction. One of them is to subtract 30 days from current date. This is completely wrong, because not every month has 30 days. Here, some developers will begin to predefine arrays to indicate the number of days in each month, which then will be used in their complicated calculations. Here is an example of this wrong approach.

echo date('Y-m-d', strtotime(date('Y-m-d')) - 60*60*24*30);

This line is full of mistakes. First of all strtotime(date(‘Y-m-d’)) can be replaced by the more elegant strtotime(‘now’), but for this later. Another big mistake is that 60*60*24*30, which is number of seconds in 30 days can be predefined as a constant. Eventually the result is wrong, because not every month has 30 days.

The Correct Approach

A small research of the problem and the functions in versions prior of 5.3.0 of PHP is needed. Typical case study of date formatting happen when working with dates from a database. The following code is a classical example. Continue reading How to Check if a Date is More or Less Than a Month Ago with PHP

Some Notes on the Object-oriented Model of PHP

PHP 5 introduces interfaces and abstract classes. To become a little clearer, let us see their definitions.


Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.
Interfaces are defined using the interface keyword, in the same way as a standard class, but without any of the methods having their contents defined.
All methods declared in an interface must be public, this is the nature of an interface.

To implement an interface, the implements operator is used. All methods in the interface must be implemented within a class; failure to do so will result in a fatal error. Classes may implement more than one interface if desired by separating each interface with a comma.

Abstract Classes

PHP 5 introduces abstract classes and methods. Classes defined as abstract may not be instantiated, and any class that contains at least one abstract method must also be abstract. Methods defined as abstract simply declare the method’s signature – they cannot define the implementation.

When inheriting from an abstract class, all methods marked abstract in the parent’s class declaration must be defined by the child; additionally, these methods must be defined with the same (or a less restricted) visibility. For example, if the abstract method is defined as protected, the function implementation must be defined as either protected or public, but not private. Furthermore the signatures of the methods must match, i.e. the type hints and the number of required arguments must be the same. This also applies to constructors as of PHP 5.4. Before 5.4 constructor signatures could differ.

Some Cases

Now let’s do a quick experiment. According to the definition of interfaces we can define an interface and than an abstract class can implement this interface.
Continue reading Some Notes on the Object-oriented Model of PHP

Thing to Know About PHP Arrays

Consider the following case. We have an array with identical keys.

$arr = array(1 => 10, 1 => 11);

What happens when the interpreter reaches this line of code? This is not a syntax error and it is completely valid. Very similar, but more interesting case is when we have an array of identical keys, where those identical keys are represented once as an integer and then as a string.

Keys in PHP arrays are not type sensitive, so pay attention when using them!
Keys in PHP arrays are not type sensitive, so pay attention when using them!

$arr = array(1 => 10, "1" => 11);

Now several questions arise. First of all, how many elements have this array? Two or one. This can be easily verified by checking what count() will return. Continue reading Thing to Know About PHP Arrays

Scroll an IFRAME Content to a Predefined Position


Usually when you use an IFRAME tag to link an external source the page that’s referenced by the SRC attributes is loaded at the top left corner. This is the default behavior, but sometimes you’d like to show to your users not the entire page from the top left corner, but to show only part of the external page instead.

In most of the cases the reference is external and you don’t have control over the external page. Thus you’ve to scroll the IFRAME content to the desired position. This of course is impossible. Yeah, there are some JavaScript hacks, but they’re all a bad solution, because the scrolling occurs only after the page is loaded.

The Solution

You can wrap the IFRAME into a div and scroll the DIV content using absolute TOP and LEFT CSS properties.

Here’s an example:

    width    : 400px;
    height   : 200px;
    overflow : hidden;
    position : relative;
    position : absolute;
    top      : -100px;
    left     : -100px;
    width    : 1280px;
    height   : 1200px;

Here you have one DIV with dimensions 400x200px. Now by moving the IFRAME within it you can position it on the right place.

<div id="my-div">
<iframe src="http://www.example.com" id="my-iframe" scrolling="no"></iframe>

Continue reading Scroll an IFRAME Content to a Predefined Position