Why Does ' ' Work Better Than NULL in This Code?

[Nobilis]

Hello!

I am following a tutorial on PHP. The code given below is to get the pages listed in the database to display to the webpage. I already fixed the problem and the code works fine.

When I used a NULL value for both variables, the $getSubj would work, and display the subject in the content page. $getPage would default to "Select A Subject or Page to Edit...". In the tutorial, of course, it worked.

I attempted to change the value to '' but that gave me an error. I changed it to " ". That failed as well. Finally, I tried ' ', and this worked. After two days of puzzling, and wonderment, I was able to move on. I changed both the value for $getPage & $getSubj for consistency. PHP doesn't seem to mind.

My question is why did ' ' finally do the trick, whereas NULL, "" and '' all failed? Why did PHP initially behave the way it did prior to replacing the values? BTW, '' is two single quotes with no space. Thank you in advance for your feedback.


Here is the function:

PHP Code:

function funcFndAll()
{
  global $getSubj;
  global $getPage;
  
 if(isset($_GET['subj']))
{
    $getSubj = funcGetSubID($_GET['subj']);
    $getPage = ' ';                //replaced NULL with ' '
    
}
elseif(isset($_GET['page']))
{
   
    $getSubj = ' ';              // replaced NULL with ' '
    $getPage = funcGetPageID($_GET['page']); 
}
else
{
    $getSubj = NULL;   
    $getPage = NULL;
}
} 


Here is the code to print that prints
the subjects and pages to navigation:

PHP Code:

<?php
          if(($getSubj != null) && ($getPage != null))
         {
                echo $getSubj['menu_name']; 
            echo $getPage['menu_name'];
         }
      else
         {
                echo "Select A Subject or Page to Edit...";
         }
?>
<div class="page-content"></div>
    
<?php echo $getPage['content']; ?>

[Wanna]

You set them as null and you check them as NULL
PHP is case sensitive

[Nobilis]

Originally Posted by Wanna

You set them as null and you check them as NULL
PHP is case sensitive

Excellent! Thank you. I am going to try making that change in my code and what happens.

[Nobilis]

Hi Wanna! Great suggestion but it didn't work. My code still did the same thing. But thank you for bringing that to my attention. I never would have caught that. Much appreciated!

[Wanna]

You are missing semicolon on the following rule:

PHP Code:

$getPage = ' '                //replaced NULL with ' ' 


change it to:

PHP Code:

$getPage = ' ';                //replaced NULL with ' ' 


[Nobilis]

Originally Posted by Wanna

You are missing semicolon on the following rule:

PHP Code:

$getPage = ' '                //replaced NULL with ' ' 


change it to:

PHP Code:

$getPage = ' ';                //replaced NULL with ' ' 


You can ignore that. I forgot the semi-colon when I typed in the code. TYVM. I fixed it in the code above.

[tangoforce]

I'm not so sure about null being case sensitive.. true and false certainly aren't..

The difference between null and '' is basically that '' is a string thats been initialised but it is empty. In other words the string has been created but it holds nothing.

Null means the string, object, whatever doesn't exist. If you tested $Var and it was null it basically means that $Var doesn't actually exist.

If thats still not quite clear, let me put it like this:
You can have a plastic container full of sweets. Thats your variable containing something.
You can have an empty container. Thats your ''
You can have no container. Thats your null.

Make sense? - You know that the container could theoretically exist (even if it doesn't) so you can test for it by testing it against null.

Also you're using ' ' in your code. ' ' is not the same as ''. ' ' contains a space character which although prints nothing on the screen it is a valid ASCII character so its not the same as an empty string.

[durangod]

And after the girl takes all your candy and container you also end up with null. LMAO tango thats some funny stuff man. too cool.

[tangoforce]

Originally Posted by durangod

And after the girl takes all your candy and container you also end up with null.

Ah no, thats when you realise you and her were speaking different languages and she actually leaves you with 'nil'

[Nobilis]

Originally Posted by tangoforce

I'm not so sure about null being case sensitive.. true and false certainly aren't..

The difference between null and '' is basically that '' is a string thats been initialised but it is empty. In other words the string has been created but it holds nothing.

Null means the string, object, whatever doesn't exist. If you tested $Var and it was null it basically means that $Var doesn't actually exist.

If thats still not quite clear, let me put it like this:
You can have a plastic container full of sweets. Thats your variable containing something.
You can have an empty container. Thats your ''
You can have no container. Thats your null.

Make sense? - You know that the container could theoretically exist (even if it doesn't) so you can test for it by testing it against null.

Also you're using ' ' in your code. ' ' is not the same as ''. ' ' contains a space character which although prints nothing on the screen it is a valid ASCII character so its not the same as an empty string.

So with ' ' I am testing for something, whereas NULL is nothing. By swapping out the values I was basically telling PHP check for something...that may come later on...is that right? If I left it at NULL I am telling PHP to test for nothing?

[tangoforce]

You're telling it to test to see if the variable is nothing yes. It's pretty much the opposite of using the isset() function as far as I know.

There may be better definitions out there but my explanation is the basic principle of it all.

[Dormilich]

Originally Posted by Wanna

You set them as null and you check them as NULL
PHP is case sensitive

nope. PHP allows you define constants as case-(in)sensitive. NULL is defined case-insensitive (ref.)

[Fou-Lu]

The biggest thing to remember is that null represents a void value of \0 regardless of datatype provided; however, null != '' (and also, != ' ' which is a string with a space in it) which differentiates between an initialized string of nothing and a variable of no value. Null is not case sensitive as it is neither a variable or a constant.
In the above situation, what you would actually have is:

PHP Code:

$a = null; // var dump will provide NULL or \0
$a = ''; // var dump will provide string(0), which equates to {''}
$a = 'hello world';
// var dump will provide string(11), which equates to {'h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd')
// C does not contain a datatype for a string, it is only a char array. 


Also, an understanding of null is critical in OOP.