Incrementing / Decrementing Operators
++
increment operator
--
decrement operator
Example Name Effect
---------------------------------------------------------------------
++$a Pre-increment Increments $a by one, then returns $a.
$a++ Post-increment Returns $a, then increments $a by one.
--$a Pre-decrement Decrements $a by one, then returns $a.
$a-- Post-decrement Returns $a, then decrements $a by one.
These can go before or after the variable.
If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.
For example:
$apples = 10;
for ($i = 0; $i < 10; ++$i) {
echo 'I have ' . $apples-- . " apples. I just ate one.\n";
}
Live example
In the case above ++$i
is used, since it is faster. $i++
would have the same results.
Pre-increment is a little bit faster because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.
However, you must use $apples--
, since first, you want to display the current number of apples, and then you want to subtract one from it.
You can also increment letters in PHP:
$i = "a";
while ($i < "c") {
echo $i++;
}
Once z
is reached aa
is next, and so on.
Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.
Stack Overflow Posts:
Notice: Undefined variable
From the vast wisdom of the PHP Manual:
Relying on the default value of an uninitialized variable is problematic in the case of including one file into another which uses the same variable name. It is also a major security risk with register_globals turned on. E_NOTICE level error is issued in case of working with uninitialized variables, however not in the case of appending elements to the uninitialized array. isset() language construct can be used to detect if a variable has been already initialized. Additionally and more ideal is the solution of empty() since it does not generate a warning or error message if the variable is not initialized.
From PHP documentation:
No warning is generated if the variable does not exist. That means
empty() is essentially the concise equivalent to !isset($var) || $var
== false.
This means that you could use only empty()
to determine if the variable is set, and in addition it checks the variable against the following, 0
, 0.0
, ""
, "0"
, null
, false
or []
.
Example:
$o = [];
@$var = ["",0,null,1,2,3,$foo,$o['myIndex']];
array_walk($var, function($v) {
echo (!isset($v) || $v == false) ? 'true ' : 'false';
echo ' ' . (empty($v) ? 'true' : 'false');
echo "\n";
});
Test the above snippet in the 3v4l.org online PHP editor
Although PHP does not require a variable declaration, it does recommend it in order to avoid some security vulnerabilities or bugs where one would forget to give a value to a variable that will be used later in the script. What PHP does in the case of undeclared variables is issue a very low level error, E_NOTICE
, one that is not even reported by default, but the Manual advises to allow during development.
Ways to deal with the issue:
Recommended: Declare your variables, for example when you try to append a string to an undefined variable. Or use isset()
/ !empty()
to check if they are declared before referencing them, as in:
//Initializing variable
$value = ""; //Initialization value; Examples
//"" When you want to append stuff later
//0 When you want to add numbers later
//isset()
$value = isset($_POST['value']) ? $_POST['value'] : '';
//empty()
$value = !empty($_POST['value']) ? $_POST['value'] : '';
This has become much cleaner as of PHP 7.0, now you can use the null coalesce operator:
// Null coalesce operator - No need to explicitly initialize the variable.
$value = $_POST['value'] ?? '';
Set a custom error handler for E_NOTICE and redirect the messages away from the standard output (maybe to a log file):
set_error_handler('myHandlerForMinorErrors', E_NOTICE | E_STRICT)
Disable E_NOTICE from reporting. A quick way to exclude just E_NOTICE
is:
error_reporting( error_reporting() & ~E_NOTICE )
Suppress the error with the @ operator.
Note: It's strongly recommended to implement just point 1.
Notice: Undefined index / Undefined offset
This notice appears when you (or PHP) try to access an undefined index of an array.
Ways to deal with the issue:
Check if the index exists before you access it. For this you can use isset()
or array_key_exists()
:
//isset()
$value = isset($array['my_index']) ? $array['my_index'] : '';
//array_key_exists()
$value = array_key_exists('my_index', $array) ? $array['my_index'] : '';
The language construct list()
may generate this when it attempts to access an array index that does not exist:
list($a, $b) = array(0 => 'a');
//or
list($one, $two) = explode(',', 'test string');
Two variables are used to access two array elements, however there is only one array element, index 0
, so this will generate:
Notice: Undefined offset: 1
$_POST
/ $_GET
/ $_SESSION
variable
The notices above appear often when working with $_POST
, $_GET
or $_SESSION
. For $_POST
and $_GET
you just have to check if the index exists or not before you use them. For $_SESSION
you have to make sure you have the session started with session_start()
and that the index also exists.
Also note that all 3 variables are superglobals and are uppercase.
Related:
Best Answer
2021 Update
You can do it with a custom unction hooked in
woocommerce_cart_item_name
action hook, this way:Code goes in function.php file of your active child theme (or theme) or also in any plugin file.
This code is tested and works on WooCommerce 3+. You will get:
And
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