I am trying to write a function to avoid getting variable undefined error. Right now, i have a code like this:
function check($str){
if(isset($str)){
$s = $str;
} else {
$s = "";
}
}
check($_GET['var']);
The get var is not set. I am getting a variable undefined error on my screen. How do i alter my function to not throw this error and just return "" if it is not set? I don't want to have to code 100 if statements to avoid getting variable undefined. Thanks.
We already have in PHP a construct to check that. It is called isset(). With it you can check whether a variable exists. If you would like to create it with some default values if it doesn't exist yet, we also have syntax for it. It's null-coalescing operator.
$_GET['var'] = $_GET['var'] ?? '';
// or since PHP 7.4
$_GET['var'] ??= '';
Although I'm not sure if it is the right way of doing it, for the sake of providing an answer you can pass the variable by reference, this allows you to get away with passing undefined variables and check if it is set inside the function..
function check(&$str){
if(!isset($str)){
$str = "not set";
}
}
check($_GET['var']);
echo $_GET['var'];
What is the proper way to do an if/else statement regarding a variable which may or may not exist?
For example: I have a website search script that gets variables from the URL. If the user has not checked any advanced options then they are not included in the URL. Basically what I'm wondering is, would it be correct to use something like the following if the variable did not exist?
if ($variable == "yes") { do stuff; }
Would this cause any sort of problems if that variable did not exist? or should I always use something like:
if (isset($variable) && $variable == "yes") { do stuff; }
try to put the if value equals in the if statement, this way you never get error notice and its correct
if(isset($value)){
if($value==='this'){
//magic
}
}
The second way imo, because it will suppress the notice error that $variable does not exist if it's not set. Either way, it's only a notice error though - so you could just suppress notices and use the first way too..
empty
No warning is generated if the variable does not exist. That means empty() is essentially the concise equivalent to !isset($var) || $var == false.
// $foo = 'no';
if(!empty($foo) AND $foo == 'yes')
{
echo $foo;
}
Before you check your variable for a value, check it with isset and set default values like
if (!isset($variable)) {
$variable = "no";
}
if ($variable == "yes") { do stuff; }
Seems an easy one, but cannot work out why:
if(!isset($_SESSION[$_REQUEST["form_id"]]))
{
//do stuff
}
reutrns
Notice: Undefined index: form_id
empty returns same response.
This has been driving me mad for a while. :)
You're calling isset for $_SESSION but as the error states the issue is with $_REQUEST['form_id'] not being set.
if (!isset($_REQUEST['form_id']) || !isset($_SESSION[$_REQUEST['form_id']])) {
That's because it resolves $_REQUEST['form_id'] first and that causes the notice. You could do this instead:
if (!isset($_REQUEST['form_id']) || !isset($_SESSION[$_REQUEST["form_id"]]))
{
//do stuff
}
please check if key exists with
array_key_exists('form_id', $_REQUEST);
before checking value with
isset($_REQUEST['form_id']);
or check if your params are empty like
<?php
if (!empty($_REQUEST['form_id'])) {
// do anything
}
else
{
// I can't find the key in array
}
?>
A new problem has arisen for me as I tried to run my script on a different PHP Server.
ON my old server the following code appears to work fine - even when no s parameter is declared.
<?php
if ($_GET['s'] == 'jwshxnsyllabus')
echo "<body onload=\"loadSyllabi('syllabus', '../syllabi/jwshxnporsyllabus.xml', '../bibliographies/jwshxnbibliography_')\">";
if ($_GET['s'] == 'aquinas')
echo "<body onload=\"loadSyllabi('syllabus', '../syllabi/AquinasSyllabus.xml')\">";
if ($_GET['s'] == 'POP2')
echo "<body onload=\"loadSyllabi('POP2')\">";
elseif ($_GET['s'] == null)
echo "<body>"
?>
But now, on a my local server on my local machine (XAMPP - Apache) I get the following error when no value for s is defined.
Notice: Undefined index: s in C:\xampp\htdocs\teaching\index.php on line 43
Notice: Undefined index: s in C:\xampp\htdocs\teaching\index.php on line 45
Notice: Undefined index: s in C:\xampp\htdocs\teaching\index.php on line 47
Notice: Undefined index: s in C:\xampp\htdocs\teaching\index.php on line 49
What I want to happen for the script to call certain javascript functions if a value is declared for s, but if nothing is declared i would like the page to load normally.
Can you help me?
Error reporting will have not included notices on the previous server which is why you haven't seen the errors.
You should be checking whether the index s actually exists in the $_GET array before attempting to use it.
Something like this would be suffice:
if (isset($_GET['s'])) {
if ($_GET['s'] == 'jwshxnsyllabus')
echo "<body onload=\"loadSyllabi('syllabus', '../syllabi/jwshxnporsyllabus.xml', '../bibliographies/jwshxnbibliography_')\">";
else if ($_GET['s'] == 'aquinas')
echo "<body onload=\"loadSyllabi('syllabus', '../syllabi/AquinasSyllabus.xml')\">";
else if ($_GET['s'] == 'POP2')
echo "<body onload=\"loadSyllabi('POP2')\">";
} else {
echo "<body>";
}
It may be beneficial (if you plan on adding more cases) to use a switch statement to make your code more readable.
switch ((isset($_GET['s']) ? $_GET['s'] : '')) {
case 'jwshxnsyllabus':
echo "<body onload=\"loadSyllabi('syllabus', '../syllabi/jwshxnporsyllabus.xml', '../bibliographies/jwshxnbibliography_')\">";
break;
case 'aquinas':
echo "<body onload=\"loadSyllabi('syllabus', '../syllabi/AquinasSyllabus.xml')\">";
break;
case 'POP2':
echo "<body onload=\"loadSyllabi('POP2')\">";
break;
default:
echo "<body>";
break;
}
EDIT: BTW, the first set of code I wrote mimics what yours is meant to do in it's entirety. Is the expected outcome of an unexpected value in ?s= meant to output no <body> tag or was this an oversight? Note that the switch will fix this by always defaulting to <body>.
Get into the habit of checking if a variable is available with isset, e.g.
if (isset($_GET['s']))
{
//do stuff that requires 's'
}
else
{
//do stuff that doesn't need 's'
}
You could disable notice reporting, but dealing them is good hygiene, and can allow you to spot problems you might otherwise miss.
I always use a utility function/class for reading from the $_GET and $_POST arrays to avoid having to always check the index exists... Something like this will do the trick.
class Input {
function get($name) {
return isset($_GET[$name]) ? $_GET[$name] : null;
}
function post($name) {
return isset($_POST[$name]) ? $_POST[$name] : null;
}
function get_post($name) {
return $this->get($name) ? $this->get($name) : $this->post($name);
}
}
$input = new Input;
$page = $input->get_post('page');
I was having the same problem in localhost with xampp. Now I'm using this combination of parameters:
// Report all errors except E_NOTICE
// This is the default value set in php.ini
error_reporting(E_ALL ^ E_NOTICE);
php.net: http://php.net/manual/pt_BR/function.error-reporting.php
First check the $_GET['s'] is set or not. Change your conditions like this
<?php
if (isset($_GET['s']) && $_GET['s'] == 'jwshxnsyllabus')
echo "<body onload=\"loadSyllabi('syllabus', '../syllabi/jwshxnporsyllabus.xml', '../bibliographies/jwshxnbibliography_')\">";
elseif (isset($_GET['s']) && $_GET['s'] == 'aquinas')
echo "<body onload=\"loadSyllabi('syllabus', '../syllabi/AquinasSyllabus.xml')\">";
elseif (isset($_GET['s']) && $_GET['s'] == 'POP2')
echo "<body onload=\"loadSyllabi('POP2')\">";
elseif (isset($_GET['s']) && $_GET['s'] == null)
echo "<body>"
?>
And also handle properly your ifelse conditions
I recommend you check your arrays before you blindly access them :
if(isset($_GET['s'])){
if ($_GET['s'] == 'jwshxnsyllabus')
/* your code here*/
}
Another (quick) fix is to disable the error reporting by writing this on the top of the script :
error_reporting(0);
In your case, it is very probable that your other server had the error reporting configuration in php.ini set to 0 as default.
By calling the error_reporting with 0 as parameter, you are turning off all notices/warnings and errors. For more details check the php manual.
Remeber that this is a quick fix and it's highly recommended to avoid errors rather than ignore them.
You should check wheter the index exists before use it (compare it)
if (isset($_GET['s']) AND $_GET['s'] == 'foobar') {
echo "foo";
}
Use E_ALL | E_STRICT while developing!
Actually none of the proposed answers, although a good practice, would remove the warning.
For the sake of correctness, I'd do the following:
function getParameter($param, $defaultValue) {
if (array_key_exists($param, $_GET)) {
$value=$_GET[$param];
return isSet($value)?$value:$defaultValue;
}
return $defaultValue;
}
This way, I check the _GET array for the key to exist without triggering the Warning. It's not a good idea to disable the warnings because a lot of times they are at least interesting to take a look.
To use the function you just do:
$myvar = getParameter("getparamer", "defaultValue")
so if the parameter exists, you get the value, and if it doesnt, you get the defaultValue.
Avoid if, else and elseifs!
$loadMethod = "";
if(isset($_GET['s'])){
switch($_GET['s']){
case 'jwshxnsyllabus':
$loadMethod = "loadSyllabi('syllabus', '../syllabi/jwshxnporsyllabus.xml', '../bibliographies/jwshxnbibliography_')";
break;
case 'aquinas':
$loadMethod = "loadSyllabi('syllabus', '../syllabi/AquinasSyllabus.xml')";
break;
case 'POP2':
$loadMethod = "loadSyllabi('POP2')";
}
}
echo '<body onload="'.$loadMethod.'">';
clean, readable code is maintainable code
Simple function, works with GET or POST. Plus you can assign a default value.
function GetPost($var,$default='') {
return isset($_GET[$var]) ? $_GET[$var] : (isset($_POST[$var]) ? $_POST[$var] : $default);
}
Another option would be to suppress the PHP undefined index notice with the # symbol in front of the GET variable like so:
$s = #$_GET['s'];
This will disable the notice. It is better to check if the variable has been set and act accordingly.
But this also works.
The real answer to this is to put a # At symbol before the variable which will suppress the error
#$_GET["field"]
#$_POST["field"]
It will work some slower, but will keep the code clean.
When something saves time for the programmer, and costs time for the website users (or requires more hardware), it depends on how much people will use it.
In PHP, depending on your error reporting level, if you don't define a constant and then call it like so:
<?= MESSAGE ?>
It may print the name of the constant instead of the value!
So, I wrote the following function to get around this problem, but I wanted to know if you know a way to do it in faster code? I mean, when I did a speed test without this function, I can define and dump 500 constants in .0073 seconds. But use this function below, and this switches to anywhere from .0159 to .0238 seconds. So, it would be great to get the microseconds down to as small as possible. And why? Because I want to use this for templating. I'm thinking there simply has to be a better way than toggling the error reporting with every variable I want to display.
function C($constant) {
$nPrev1 = error_reporting(E_ALL);
$sPrev2 = ini_set('display_errors', '0');
$sTest = defined($constant) ? 'defined' : 'not defined';
$oTest = (object) error_get_last();
error_reporting($nPrev1);
ini_set('display_errors', $sPrev2);
if (strpos($oTest->message, 'undefined constant')>0) {
return '';
} else {
return $constant;
}
}
<?= C(MESSAGE) ?>
As long as you don't mind using quotes on your constants, you can do this:
function C($constant) {
return defined($constant) ? constant($constant) : 'Undefined';
}
echo C('MESSAGE') . '<br />';
define('MESSAGE', 'test');
echo C('MESSAGE') . '<br />';
Output:
Undefined
test
Otherwise, there's no way around it without catching the notice thrown by using an undefined constant.
try
if (isset(constant($constant)) ...
This shouldn't trigger any E_NOTICE messages, so you don't have to set and reset error_reporting.