php function trouble

[rbush]

I am trying to create a function to load a file only once, then I want to call it multiple times in my code but it doesn't seem to be working.
here is my function:

<?php
    function load_sw_popup($xml){
    $xml=simplexml_load_file("sw-popup.xml");
    }
?>

an example of one of the places I am calling it:

<?php
       load_sw_popup($xml);
       echo $xml->recentPRs;
?>

[jscheuer1]

By declaring $xml inside a function, I believe it's only available inside that function. If your desire is to create a GLOBAL, don't use a function. Instead just do:

$xml=simplexml_load_file("sw-popup.xml"); 

Then later for your other code, just do:

<?php 
       echo $xml->recentPRs; 
?>

I think there are ways to have the function make a GLOBAL though, check global in the man:

http://php.net/manual/en/language.variables.scope.php

It shows how to take a GLOBAL and act on it in a function. It might be able to be used to create a GLOBAL in a function. But, as I said, if you want a GLOBAL, the easiest thing is to just not use a function to create it. I think this would do it though:

<?php  
    function load_sw_popup(){  
        $GLOBALS['xml']=simplexml_load_file("sw-popup.xml");
    }  
?>

Then later:

<?php 
       load_sw_popup(); 
       echo $xml->recentPRs; 
?>

[rbush]

Thanks for your help!

[Nile]

Actually, better than using a global variable (which is normally advised against), it's probably better just to use a reference.

<?php 
function load_sw_popup(&$xml){ 
    $xml = simplexml_load_file("sw-popup.xml"); 
} 
?>

[jscheuer1]

Nile, I may be missing something but I just tested that and it appears to simply be another syntax for creating a global variable:

<?php  
    function load_sw_popup(&$xml){ 
        $xml='bob';  
    } 
    load_sw_popup($xml); 
    echo $GLOBALS['xml']; //echoes bob
?>

[djr33]

It's a fairly complicated topic:
http://php.net/manual/en/language.references.pass.php
The basic idea: you can send a variable into a function and actually manipulate it in that function. It's sort of like saying "pretend this isn't a new scope". But it's not global, because that can be within a few levels. This becomes relevant if you call functions from within functions, or, often, with OOP.

It's not equivalent. You'll see that no longer works when embedded:

 <?php  
    function load_sw_popup(&$xml){ 
        $xml='bob';  
    } 
    function savebob() {
        load_sw_popup($xml); 
    }
    savebob();
    echo $GLOBALS['xml']; //echoes nothing, or gives an error
?>

(You were coincidentally already in global scope. This is an example of why scope can be confusing.)

Global variables should be used for system settings, for something that should always be set. (One problem can come from mixing in third-party scripts, in case of a name conflict, but that situation is relatively rare, not that it's easy to fix if it happens.)
Global variables should not be used just to get a value from one thing to another. Personally I strongly prefer to use return to do all of this if possible. I don't really like using 'reference' unless required, and it usually isn't.

[jscheuer1]

It is equivalent for the example as first presented by Nile. In your example $xml isn't accessible anywhere I can see. You would have to make a getter function and/or $xml would have to be assigned as a property of something in order to be both accessible and not global.

In my previous post I was going to add something like:

To avoid using global variables you have to carry out whatever you are doing within the context of an object or function.

In other words, just using &$whatever doesn't prevent a global variable from being created. It's the context or scope of the function or object that determines that. But that wasn't the original question. Essentially the OP had created $xml in a limited local scope and was wondering why it wasn't available in the global scope.

[djr33]

$xml would be available within the savebob() function. That's why it's not global. But it's the same $xml variable then within savebob() and also load_sw_popup() because it's sent by reference to load_sw_popup().
I was just replying to your reply to Nile to clear that up.


As for the original question, I think it would be solved most simply like this:

 <?php
    function load_sw_popup(){
        return simplexml_load_file("sw-popup.xml");
    }
?>

<?php
       $xml = load_sw_popup();
       echo $xml->recentPRs;
?>

Simple as that. At least that solves the immediate problem.

[traq]

If part of the original question is loading the file only once, here's how you could modify Daniel's function to do it:

 <?php

    // this causes the function to load the xml file
    $xml = load_or_get_sw_popup();

    // this causes the function to return the previously loaded xml file
    // (it does _not_ load it again)
    $xml2 = load_or_get_sw_popup();

    function load_sw_popup(){
        // static variables persist (are not destroyed) between function calls
        static $xml;
        // if this is the first time we call the function, $xml will be NULL
        if( ! $xml ){
            // so we load the file
            $xml = simplexml_load_file("sw-popup.xml");
        }
        return $xml;
    }

[jscheuer1]

If part of the original question is loading the file only once

Yes, I was wondering that too.