oop questions

drag0n

hi:
i have just started to use oop in php... and i have a few questions.

what is the difference between "private function _construct()" and "private function className()"? Can I use either one to create the constructor?

i have been using a mysql wrapper class for all my mysql operations; and one of the functions of this class is to open mysql connections. alot of my functions within my user class deals with the db. I am wondering which would be more effective: putting the "$db = new MySQL; $db->Open();" only in the constructor so its initiated for the entire class or initiating it each time in each function that needs db access?

Can I call session_start(); only in the page that is including the class file or must I call the function inside the class file? I am a bit confused about what transfers over to the class file when it is included in a php script. For example if before including the class file I included config file with global variables; can I use those global variables in the class file or must I include the config file in the class file to use the vars? also; even if I do include a file with lots of variables inside the class file; how do i use those variables within the class? it seems like I cant just call variables from outside the class.

Thanks

NogDog

drag0n;10890785 wrote:
hi:
i have just started to use oop in php... and i have a few questions.

what is the difference between "private function _construct()" and "private function className()"? Can I use either one to create the constructor?

Functionally there is no difference that I know of. Practically speaking, by using __construct() you do not need to worry about renaming the constructor method should you decide at some point to rename the class.

i have been using a mysql wrapper class for all my mysql operations; and one of the functions of this class is to open mysql connections. alot of my functions within my user class deals with the db. I am wondering which would be more effective: putting the "$db = new MySQL; $db->Open();" only in the constructor so its initiated for the entire class or initiating it each time in each function that needs db access?

Unless you have some specific reason for using multiple connections, I would recommend just using a single, initial connection in order to avoid unnecessary processing.

Also; a newb question... why must we always use "==" when checking for values in if statements? In most other languages I can use a single "=" when checking for boolean values; but in PHP you have to use == for everything. Does that mean we dont ever use a single = when checking variables?

Thanks

"=" is an assignment operator, "==" is a comparison operator; therefore they have very different purposes and uses. By not overloading the "=" operator with both functions, it allows you to use both within a larger expression without any ambiguity, e.g.:

if(($count = $count + 1) == 100)
{
   break;
}

(That's a somewhat silly example, but it's the first thing I thought of.)

NogDog

drag0n;10890785 wrote:
...
Can I call session_start(); only in the page that is including the class file or must I call the function inside the class file? I am a bit confused about what transfers over to the class file when it is included in a php script. For example if before including the class file I included config file with global variables; can I use those global variables in the class file or must I include the config file in the class file to use the vars?

When you include/require a file, it is as if the text in that file were inserted into the file doing the inclusion right at that point. So any globals already defined will be available to the included file, and globals defined after the include/require will not be available.

session_start() only needs to be executed once per page request, regardless of how many files it includes. The only restrictions are that it be called before any output is generated and before any reference is made to the $_SESSION array. Whether the session_start() is in the main script or one of the include files is dependent upon how you want to organize your application.

Weedpacket

drag0n wrote:
what is the difference between "private function _construct()" and "private function className()"? Can I use either one to create the constructor?

As NogDog notes, there's no difference in functionality. "className()" was used in PHP 4, "construct()" was introduced in PHP 5. PHP will look for "construct()" first, and if it can't find it, will look for "className()" instead. In the words of the manual:

For backwards compatibility, if PHP 5 cannot find a __construct() function for a given class, it will search for the old-style constructor function, by the name of the class

drag0n

NogDog;10890793 wrote:
When you include/require a file, it is as if the text in that file were inserted into the file doing the inclusion right at that point. So any globals already defined will be available to the included file, and globals defined after the include/require will not be available.

session_start() only needs to be executed once per page request, regardless of how many files it includes. The only restrictions are that it be called before any output is generated and before any reference is made to the $_SESSION array. Whether the session_start() is in the main script or one of the include files is dependent upon how you want to organize your application.

So what about variables that are initialized outside of the class? For example:

$var = "x";

class myClass {
public function myClass() {
echo $var;
}
}

How can I use $var inside the class? The above code does not work. It doesnt seem like the $var is accessible inside the class even though its inside the same file.

NogDog

class MyClass {
   private $var;
   public function __construct($var)
   {
      $this->var = $var;
   }
   public function output()
   {
      echo $this->var;
   }
}

$var = "Hello, World.";
$test = new MyClass($var);
$test->output();

Weedpacket

It doesnt seem like the $var is accessible inside the class even though its inside the same file.

But it's inside a function.