[Resolved] references and global scope problem

[Bloodwine]

function test() {
   global $a; 
   $a = 'foo';
   $b = 'bar';
   $a =& $b;
}
test();
echo $a."\n"; // prints out 'foo' instead of expected 'bar'

Is this because references aren't pointers? Is there a workaround?

The real code involves an object being used as a variable store (to avoid polluting the global namespcae), but I am assigning (by reference) backwards-compatable global variables for use in third-party code so it doesn't break when I perform the upgrade.

[paulnaj]

Hi bloodwine,

You probably know that the function does what's expected if you take the '&' out of the $a =& $b; line.

So why not just do that? Unless I've missed something, the $b is surely defined in a 'local' function scope, so it shouldn't affect the global namespace at all anyway.

Paul.

[Bloodwine]

sorry, my test case isn't exactly indicative of my needs. I was just trying to illustrate the failure of assigning a global pointer within a function.

The availability (or lack thereof) of $b in the global namespace is not the issue.

I will tell you about my real-world needs.

I have several global arrays used by my application, such as $CONFIG, $CACHE, $_THEME, etc.

within each file and/or function I go a "global $_CONFIG" (or what-have-you) to ensure they are available.

My newer, more elegant code uses an object to store all the variables to prevent pollution of the global namespace. Granted, I still have to keep track of one global variable (the object), but it's at least somewhat cleaner.

For example:

$_VARS = new VarStore;
$_VARS->addVar('_CONFIG', array());

these variables are public, and do not require using a class method to retreive their values, but one can be used if wanting to perform certain checks (existence, type, etc.)

But usually they are manipulated via:
$VARS->variables['CONFIG']['db_name'] = 'mydatabase';
$VARS->variables['THEME']['site_col_bg'] = '#ffffff';

and so forth..

but so that existing third-party code is not broken, I am trying to reference the new Variable Store arrays with the old global arrays

for example, in the top of my config.php file I may have:

global $_VARS;
$_VARS->addVar('_CONFIG', array());
global $_CONFIG;
$_CONFIG =& $_VARS->variables['_CONFIG'];

the problem is that if I try to read $_CONFIG in any other scope it is empty, and if I were to do something like:

global $_VARS;
$_VARS->addVar('_CONFIG', array());
global $_CONFIG;
$_CONFIG = 'dummy value';
$_CONFIG =& $_VARS->variables['_CONFIG'];

and elsewhere do:

global $_CONFIG;
echo $_CONFIG;

it would be 'dummy_value' instead of 'Array'

does this make any sense? I'm not the best at trying to explain things. Apologies.

[paulnaj]

Hi again,

OK, I might have a solution.

I tend to use the $GLOBALS array in functions, rather than the global statement. I just find it a little easier to read ... I didn't think it would have consequences.

Anyway, using your original example for simplicity, here's how I might've done it ...

<?php

function test() { 
   $GLOBALS['a'] = 'foo';
   $GLOBALS['b'] = 'bar';
   $GLOBALS['a'] =& $GLOBALS['b']; 
} 
test(); 
echo '$a = '.$a.'<br />'; 
echo '$b = '.$b.'<br />'; 

?>

... lo and behold!, it does the expected. I really can't work out what the actual difference between yours and mine is, but you might want to see if it works for your actual problem.

Paul 🙂

[Bloodwine]

wow, that is weird. I changed my test code to use $GLOBALS[] and it worked as expected (just as you said).

Thank you very much for your input, as that is an approach that I probably would have not tried on my own.

Maybe has to do with the fact that $GLOBALS is a super-global and scope is never an issue or maybe is a semi-obscure PHP bug.

Either way, I tip my hat to you.

[Bloodwine]

ok, I figured out the difference. I'll share in case anybody else does a search in the future on this problem.

when using "global" or "static" on a variable it actually creates a reference to that variable.

so "global $var" is a reference to the variable "$var" in the global scope. I guess that is why trying to assign a reference to that variable is an exercise in futility.

$b = 1;
global $a; // creates a local reference to $a in the global scope
$a =& $b; // does not work (just re-assigns local $a reference)

$GLOBALS["a"] =& $b; //works just fine

thank goodness for superglobal arrays!!

so I guess

global $a;

is roughly the same as

$a =& $GLOBALS["a"];