Using reference value as default param in PHP Function

Question

I'm looking to do this:

/* example filename: config_load.php */

$config_file = "c:\path\to\file.php";

function read_config($file = &$config_file)
{
$settings = array();
$doc = new DOMDocument('1.0');
$doc->load($file); 
$xpath = new DOMXPath($doc); 
$all=$xpath->query('appSettings/add');
foreach ($all as $setting) {$settings[$setting->getAttribute('key')]=$setting->getAttribute('value');}

return $settings;
}

/* end config_load.php */

So then when I actually call the file, it'd go like this -

require_once "config_load.php";
// $config_file = "c:\path\to\file2.php"; //could also do this
$config = read_config();

This way if I don't specify a file, it's going to read the default config file. I could also define $config_file anywhere before I make the function call. And someone without access to the config_load file need not worry about being able to load a different file, they can define it anywhere before they make the read_config() call.

Possible duplicate of How to set a PHP function's param to a variable as the default value — vstm
– vstm, Commented May 25, 2012 at 13:18

Jeroen · Accepted Answer · 2012-05-25 13:41:56Z

0

It's not possible:

The default value must be a constant expression, not (for example) a variable, a class member or a function call.

~ http://www.php.net/manual/en/functions.arguments.php#functions.arguments.default

However, you can get around it like this:

function read_config($file = false) {
    global $config_file;
    if ($file === false) $file = $config_file;

    $settings = array();
    $doc = new DOMDocument('1.0');
    $doc->load($file); 
    $xpath = new DOMXPath($doc); 
    $all=$xpath->query('appSettings/add');
    foreach ($all as $setting) {$settings[$setting->getAttribute('key')]=$setting->getAttribute('value');}

    return $settings;
}

or like this:

function read_config($file = false, $config_file = false) {
    if ($file === false && $config_file !== false) $file = $config_file;

    $settings = array();
    $doc = new DOMDocument('1.0');
    $doc->load($file); 
    $xpath = new DOMXPath($doc); 
    $all=$xpath->query('appSettings/add');
    foreach ($all as $setting) {$settings[$setting->getAttribute('key')]=$setting->getAttribute('value');}

    return $settings;
}

edited May 25, 2012 at 13:41

answered May 25, 2012 at 13:20

Jeroen

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3 Comments

Josh L Over a year ago

So I've got to use a global - that's the only way to do this?

Jeroen Over a year ago

Added explanation + other option

Josh L Over a year ago

Any idea why I can't get this to work with a constant? I'm trying define("CONFIG_FILE", "c:\path\file.php"); function read_config($file = CONFIG_FILE){code}; and calling with read_config(), and no luck. Constant seems like the better option here.

Bogo · Accepted Answer · 2012-05-25 13:46:21Z

-1

Yes you can:

<?php

$greet = function()
{
   return "Hello";
};

$a = $greet();
echo $a;
?>

Read more here: http://php.net/manual/en/functions.anonymous.php

answered May 25, 2012 at 13:46

Bogo

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1 Comment

Josh L Over a year ago

And how would I possibly use this?

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