“Notice: Undefined variable”, “Notice: Undefined i

Question

I'm running a PHP script and continue to receive errors like:

Notice: Undefined variable: my_variable_name in C:\wamp\www\mypath\index.php on line 10

Notice: Undefined index: my_index C:\wamp\www\mypath\index.php on line 11

Line 10 and 11 looks like this:

echo "My variable value is: " . $my_variable_name;
echo "My index value is: " . $my_array["my_index"];

What is the meaning of these error messages?

Why do they appear all of a sudden? I used to use this script for years and I've never had any problem.

How do I fix them?

---

_{This is a General Reference question for people to link to as duplicate, instead of having to explain the issue over and over again. I feel this is necessary because most real-world answers on this issue are very specific.}

_{Related Meta discussion:}

• _{What can be done about repetitive questions?}
• _{Do “reference questions” make sense?}

Answer 1

Another reason why an undefined index notice will be thrown, would be that a column was omitted from a database query.

I.e.:

$query = "SELECT col1 FROM table WHERE col_x = ?";

Then trying to access more columns/rows inside a loop.

I.e.:

print_r($row['col1']);
print_r($row['col2']); // undefined index thrown

or in a while loop:

while( $row = fetching_function($query) ) {

    echo $row['col1'];
    echo "<br>";
    echo $row['col2']; // undefined index thrown
    echo "<br>";
    echo $row['col3']; // undefined index thrown

}

Something else that needs to be noted is that on a *NIX OS and Mac OS X, things are case-sensitive.

Consult the followning Q&A's on Stack:

• Are table names in MySQL case sensitive?

• mysql case sensitive table names in queries

• MySql - Case Sensitive issue of tables in different server

Answer 2

One common cause of a variable not existing after an HTML form has been submitted is the form element is not contained within a <form> tag:

Example: Element not contained within the <form>

<form action="example.php" method="post">
    <p>
        <input type="text" name="name" />
        <input type="submit" value="Submit" />
    </p>
</form>

<select name="choice">
    <option value="choice1">choice 1</option>
    <option value="choice2">choice 2</option>
    <option value="choice3">choice 3</option>
    <option value="choice4">choice 4</option>
</select>

Example: Element now contained within the <form>

<form action="example.php" method="post">
    <select name="choice">
        <option value="choice1">choice 1</option>
        <option value="choice2">choice 2</option>
        <option value="choice3">choice 3</option>
        <option value="choice4">choice 4</option>
    </select>
    <p>
        <input type="text" name="name" />
        <input type="submit" value="Submit" />
    </p>
</form>

Answer 3

In PHP you need fist to define the variable after that you can use it.
We can check variable is defined or not in very efficient way!.

//If you only want to check variable has value and value has true and false value.
//But variable must be defined first.

if($my_variable_name){

}

//If you want to check variable is define or undefine
//Isset() does not check that variable has true or false value
//But it check null value of variable
if(isset($my_variable_name)){

}

Simple Explanation

//It will work with :- true,false,NULL
$defineVarialbe = false;
if($defineVarialbe){
    echo "true";
}else{
    echo "false";
}

//It will check variable is define or not and variable has null value.
if(isset($unDefineVarialbe)){
    echo "true";
}else{
    echo "false";
}

Answer 4

If working with classes you need to make sure you reference member variables using $this:

class Person
{
    protected $firstName;
    protected $lastName;

    public function setFullName($first, $last)
    {
        // Correct
        $this->firstName = $first;

        // Incorrect
        $lastName = $last;

        // Incorrect
        $this->$lastName = $last;
    }
}

Answer 5

Error display @ operator

For undesired and redundant notices, one could use the dedicated @ operator to »hide« undefined variable/index messages.

$var = @($_GET["optional_param"]);

• This is usually discouraged. Newcomers tend to way overuse it.
• It's very inappropriate for code deep within the application logic (ignoring undeclared variables where you shouldn't), e.g. for function parameters, or in loops.
• There's one upside over the isset?: or ?? super-supression however. Notices still can get logged. And one may resurrect @-hidden notices with: set_error_handler("var_dump");
  • Additonally you shouldn't habitually use/recommend if (isset($_POST["shubmit"])) in your initial code.
  • Newcomers won't spot such typos. It just deprives you of PHPs Notices for those very cases. Add @ or isset only after verifying functionality.

  • Fix the cause first. Not the notices.

• @ is mainly acceptable for $_GET/$_POST input parameters, specifically if they're optional.

And since this covers the majority of such questions, let's expand on the most common causes:

$_GET / $_POST / $_REQUEST undefined input

• First thing you do when encountering an undefined index/offset, is check for typos:
  $count = $_GET["whatnow?"];

  • Is this an expected key name and present on each page request?
  • Variable names and array indicies are case-sensitive in PHP.

• Secondly, if the notice doesn't have an obvious cause, use var_dump or print_r to verify all input arrays for their curent content:

  var_dump($_GET);
  var_dump($_POST);
  //print_r($_REQUEST);
  

  Both will reveal if your script was invoked with the right or any parameters at all.

• Alternativey or additionally use your browser devtools (F12) and inspect the network tab for requests and parameters:

  

  POST parameters and GET input will be be shown separately.

• For $_GET parameters you can also peek at the QUERY_STRING in

  print_r($_SERVER);
  

  PHP has some rules to coalesce non-standard parameter names into the superglobals. Apache might do some rewriting as well. You can also look at supplied raw $_COOKIES and other HTTP request headers that way.

• More obviously look at your browser address bar for GET parameters:

  http://example.org/script.php?id=5&sort=desc

  The name=value pairs after the ? question mark are your query (GET) parameters. Thus this URL could only possibly yield $_GET["id"] and $_GET["sort"].

• Finally check your <form> and <input> declarations, if you expect a parameter but receive none.

  • Ensure each required input has an <input name=FOO>
  • The id= or title= attribute does not suffice.
  • A method=POST form ought to populate $_POST.
  • Whereas a method=GET (or leaving it out) would yield $_GET variables.
  • It's also possible for a form to supply action=script.php?get=param via $_GET and the remaining method=POST fields in $_POST alongside.
  • With modern PHP configurations (≥ 5.6) it has become feasible (not fashionable) to use $_REQUEST['vars'] again, which mashes GET and POST params.

• If you are employing mod_rewrite, then you should check both the access.log as well as enable the RewriteLog to figure out absent parameters.

$_FILES

• The same sanity checks apply to file uploads and $_FILES["formname"].
• Moreover check for enctype=multipart/form-data
• As well as method=POST in your <form> declaration.
• See also: PHP Undefined index error $_FILES?

$_COOKIE

• The $_COOKIE array is never populated right after setcookie(), but only on any followup HTTP request.
• Additionally their validity times out, they could be constraint to subdomains or individual paths, and user and browser can just reject or delete them.

Answer 6

I use all time own useful function exst() which automatically declare variables.

Your code will be -

$greeting = "Hello, ".exst($user_name, 'Visitor')." from ".exst($user_location);


/** 
 * Function exst() - Checks if the variable has been set 
 * (copy/paste it in any place of your code)
 * 
 * If the variable is set and not empty returns the variable (no transformation)
 * If the variable is not set or empty, returns the $default value
 *
 * @param  mixed $var
 * @param  mixed $default
 * 
 * @return mixed 
 */

function exst( & $var, $default = "")
{
    $t = "";
    if ( !isset($var)  || !$var ) {
        if (isset($default) && $default != "") $t = $default;
    }
    else  {  
        $t = $var;
    }
    if (is_string($t)) $t = trim($t);
    return $t;
}