A little unclear about "global" keyword...

Dave · 06-08-2008, 12:06 AM

I'm a little confused about the "global" keyword (not the $GLOBALS keyword).

Example in "main" part of a PHP script:

global $sun ;
$sun = "star" ;

I think the following statement is true, but is it?

If I write a user-defined function, I must again name the var $sun to be a global within the UDF in order for it to be available to use in the function (unless I pass it to the UDF as a parameter).

Thanks,
Dave

Village Idiot · 06-08-2008, 12:23 AM

It has to do with variable scopes. Look at the following code

PHP Code:


			
<?php
function seta()
{
    $a = "Hello There";
}

seta();
echo $a;
?>

That will output nothing because $a is not in a scope for the code outside the UDF to access. Now look at this code

PHP Code:


			
<?php
function seta()
{
    global $a = "Hello There";
}

seta();
echo $a;
?>

That code will echo the value that $a was assigned to in the function.

Dave · 06-08-2008, 11:34 AM

Right, thanks, but my question was asking if this is true or if this is false:

"If I write a user-defined function, I must again name the var $sun to be a global within the UDF in order for it to be available to use in the function (unless I pass it to the UDF as a parameter)."

If it is TRUE, what is the rationale of having to "rename" $sun as a global within the context of a UDF?

Thanks again,
Dave

xenon · 06-08-2008, 01:52 PM

It's not called renaming, it's simply a statement to help the parser understand what is the variable that needs to be modified (is it coming from the namespace or is it coming from the current function -- the latter is assumed by default).

PHP Code:


			
$a = 5;

function showA()
{
    global $a; // not renaming anything, just letting the parser know that the $a is declared globally, and use its value, instead of defining a function-level variable called $a

    $a = 10;
}

showA();
echo $a; // will output 10, but if you remove the global statement (or comment it), it will output 5, of course

Dave · 06-08-2008, 03:44 PM

Thanks, although... I'm still not asking the question correctly, I guess, which again proves that I'm far from the sharpest tool in the shed.

I'll try again later after I've put some more study in this.

Appreciatively,

Dave

delayedinsanity · 06-08-2008, 04:42 PM

If I get you right, you're asking why, if you've already declared a variable as global once in a script, would you have to redeclare it as global anywhere else, as in, once you've stated it's a global, how come the entire script just doesn't immediately recognize it as a global? I *think* this may be explained by how the global keyword is working.

Technically all variables defined outside of a function are considered 'global'. They can be used anywhere within the script, including from within a function so long as you access them via the $GLOBALS array or with the global keyword. This is because functions are almost like a private namespace, where anything you do inside of them is seperate from the global scope of the script. So when you do;

PHP Code:


			
function globalVars() {
    global $szString;
    echo $szString;

    //or

    echo $GLOBALS['szString'];
}

...you're not actually renaming or redeclaring $szString as a global, you're just telling the function itself to use the global version of $szString as opposed to it's own local copy. Thus why you have to do it in every UDF you're using it in, because you're telling those specific functions to use the global copy instead of their own copy.

Was that even remotely closer to what you were looking for?
-m