DEFINE and GLOBAL variables in PHP

Jeyaseelansarc · #1 (**permalink**) 05-12-2008, 02:29 AM

Hi All,
What is the exact roll of DEFINE and GLOBAL variable in PHP?

Jeyaseelansarc · #2 (**permalink**) 05-14-2008, 11:32 PM

Hi,

define - Defines a named constant.
Global - An associative array containing references to all variables which are currently defined in the global scope of the script. The variable names are the keys of the array.

This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. You don't need to do a global $GLOBALS; to access it within functions or methods.

Jeyaseelansarc · #3 (**permalink**) 05-21-2008, 09:13 PM

Example for Defining Constants

PHP Code:

  <?php

define("CONSTANT", "Hello world.");

echo CONSTANT; // outputs "Hello world."

echo Constant; // outputs "Constant" and issues a notice.

?>

Jeyaseelansarc · #4 (**permalink**) 05-21-2008, 09:15 PM

Here another example

PHP Code:

  <?php

define("GREETING", "Hello you.", true);

echo GREETING; // outputs "Hello you."

echo Greeting; // outputs "Hello you."

 
?>

Jeyaseelansarc · #5 (**permalink**) 05-22-2008, 11:23 PM

defined function used to check whether a given named constant exists

PHP Code:

  <?php

/* Note the use of quotes, this is important.  This example is checking 

 * if the string 'CONSTANT' is the name of a constant named CONSTANT */

if (defined('CONSTANT')) {

    echo CONSTANT;

}

?>

Jeyaseelansarc · #6 (**permalink**) 05-22-2008, 11:24 PM

get_defined_constants -- Returns an associative array with the names of all the constants and their values

PHP Code:

  <?php

print_r(get_defined_constants());

?>

will print a list like:

Code:

Array
(
    [E_ERROR] => 1
    [E_WARNING] => 2
    [E_PARSE] => 4
    [E_NOTICE] => 8
    [E_CORE_ERROR] => 16
    [E_CORE_WARNING] => 32
    [E_COMPILE_ERROR] => 64
    [E_COMPILE_WARNING] => 128
    [E_USER_ERROR] => 256
    [E_USER_WARNING] => 512
    [E_USER_NOTICE] => 1024
    [E_ALL] => 2047
    [TRUE] => 1
)

Jeyaseelansarc · #7 (**permalink**) 05-22-2008, 11:27 PM

get_defined_functions

PHP Code:

  <?php

function myrow($id, $data) 

{

    return "<tr><th>$id</th><td>$data</td></tr>\n";

}

 
$arr = get_defined_functions();

 
print_r($arr);

?>

Will output something along the lines of:

Code:

Array
(
    [internal] => Array
        (
            [0] => zend_version
            [1] => func_num_args
            [2] => func_get_arg
            [3] => func_get_args
            [4] => strlen
            [5] => strcmp
            [6] => strncmp
            ...
            [750] => bcscale
            [751] => bccomp
        )

    [user] => Array
        (
            [0] => myrow
        )

)

Jeyaseelansarc · #8 (**permalink**) 06-02-2008, 03:19 AM

Whenever you're developing a new large-scale PHP script, you're bound to use global variables, since some data needs to be used by multiple parts of your script. Good examples of global data are script settings, database connections, user credentials and more. There are many ways of making this data global, but the most commonly used way is to use the global keyword, which we will explore later on in this article.

Jeyaseelansarc · #9 (**permalink**) 06-02-2008, 03:20 AM

The only problem with the global keyword, and any global data for that matter, is that's it's actually a very bad way of programming, and usually tends to lead to bigger problems later on. The reason for this is that global data ties all the separate parts of your script together, and often if you make a change in one part, something else will break in another part. If you have more than a few global variables, you're whole script will eventually become a big kludge of unmaintainable code.

Jeyaseelansarc · #10 (**permalink**) 06-02-2008, 03:20 AM

By default PHP defines a few variables called Superglobals which are automatically global, and can be accessed anywhere, like the $_GET or $_REQUEST variables. These are mainly used to retrieve form data or other outside data, and there's no real harm in using these variables, since they should never be written to anyway.

Miakoda · #11 (**permalink**) 07-12-2008, 03:16 AM

$a = 1; /* global scope */

function Test()
{
echo $a; /* reference to local scope variable */
}

Test();

the value of a in full program will be 1 because that is declare as global scope.

Jeyaseelansarc · #12 (**permalink**) 07-14-2008, 12:48 AM

Hi,
I think the above code will not be working..

madhuri_vats · #13 (**permalink**) 07-22-2008, 02:57 AM

global $a = 1; /* global scope */

function Test()
{
echo $a; /* reference to local scope variable */
}

Test();

now this willl work

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