August 2008

This warning happens only if you try to use foreach on a non array like:

$myvar = 10;
foreach ($myvar as $value) {}

If you run this, you will get:

Warning: Invalid argument supplied for foreach() in YOUR_FILE on line FOREACH_LINE

To fix this just cast $myvar to array like this:

$myvar = 10;
foreach ((array) $myvar as $value) {}

Recently I read somewhere that you can’t do this and you have to use this awful syntax:

foreach ($array as &$value) {}

This is only valid in PHP5 and can have very bad consequences for example run this piece of code:

<pre><?php
$array = array(1, 2, 3, 4, 5);
foreach ($array as &$value) {
	echo "$value \n";
}
echo "\n\n";
foreach ($array as $value) {
	echo "$value \n";
}
?>

Here first foreach loop is foreach by reference but the second one is a normal foreach loop.
Run it and see what happens.

The way to change the elements using foreach is very simple actually, the only thing you need is a $key along with the $value!

/* Filter the input */
foreach ($_POST as $key => $value) {
   $_POST[ $key ] = trim(strip_tags($value));
}

Developing better applications requires practice and study but there are little things you can do while you develop your applications that will help.

One of the things I think is very important and all great PHP developers do this is developing your application with error_reporting(E_ALL);

You have to simply place these lines on top of your PHP source files: (or put it on top of your common include file, hopefully you have one)

ini_set('display_errors', 1); /* Output all errors as oppose to logging them */
error_reporting(E_ALL);     /* Show all errors */

What this does is that it will ask PHP to show you all the errors (almost, later on this) such as warnings and notices. (It is most likely that PHP is already set to show you parser and fatal errors.)

Warnings are very important to address, they are run time errors but the compiler doesn’t halt the execution of the script.
Notices are most likely logical errors (in my experience). If you develop with error_reporting set to E_ALL you will see that PHP was telling you where the problems that took you 5 hours to find were all along.

Here is how to produce a notice and how it can help you with some problems.

Suppose you have this self submitting form:

<?php
error_reporting(0);
 
if (isset ($_POST['name'])) :
 
?>
 <form action="" method="post">
 Enter your name:
 <input type="text" name="name" /><br />
 <input type="submit" />
 </form>
<?php
 
else: /* This is the alternate PHP syntax */
 
    echo 'Hello and welcome ' .htmlentities($_POST['name1'], ENT_QUOTES);
 
endif; /* This syntax will make your templates more readable */
?>

This won’t work, you might have spotted the issue but if you didn’t, you will see that this doesn’t work.
What it does is it turns error reporting off completely on line 2 and this is where the problem is (well, not the problem itself) because if you change line 2 to:

echo 'Hello and welcome ' .htmlentities(@$_POST['name'], ENT_QUOTES);