Invalid argument supplied for foreach()

Question

It often happens to me to handle data that can be either an array or a null variable and to feed some foreach with these data.

$values = get_values();

foreach ($values as $value){
  ...
}

When you feed a foreach with data that are not an array, you get a warning:

Warning: Invalid argument supplied for foreach() in [...]

Assuming it's not possible to refactor the get_values() function to always return an array (backward compatibility, not available source code, whatever other reason), I'm wondering which is the cleanest and most efficient way to avoid these warnings:

• Casting $values to array
• Initializing $values to array
• Wrapping the foreach with an if
• Other (please suggest)

Answer 1

Personally I find this to be the most clean - not sure if it's the most efficient, mind!

if (is_array($values) || is_object($values))
{
    foreach ($values as $value)
    {
        ...
    }
}

The reason for my preference is it doesn't allocate an empty array when you've got nothing to begin with anyway.

Answer 2

How about this one? It's a lot cleaner and all in single line.

foreach ((array) $items as $item) {
 // ...
 }

Answer 3

I usually use a construct similar to this:

/**
 * Determine if a variable is iterable. i.e. can be used to loop over.
 *
 * @return bool
 */
function is_iterable($var)
{
    return $var !== null 
        && (is_array($var) 
            || $var instanceof Traversable 
            || $var instanceof Iterator 
            || $var instanceof IteratorAggregate
            );
}

$values = get_values();

if (is_iterable($values))
{
    foreach ($values as $value)
    {
        // do stuff...
    }
}

Note that this particular version is not tested, its typed directly into SO from memory.

Edit: added Traversable check

Answer 4

Please do not depend on casting as a solution, even though others are suggesting this as a valid option to prevent an error, it might cause another one.

Be aware: If you expect a specific form of array to be returned, this might fail you. More checks are required for that.

E.g. casting a boolean to an array (array)bool, will NOT result in an empty array, but an array with one element containing the boolean value as an int: [0=>0] or [0=>1].

I wrote a quick test to present this problem. (Here is a backup Test in case the first test url fails.)

Included are tests for: null, false, true, a class, an array and undefined.

---

Always test your input before using it in foreach. Suggestions:

1. Quick type checking: $array = is_array($var) or is_object($var) ? $var : [] ;
2. Type hinting arrays in methods before using a foreach and specifying return types
3. Wrapping foreach within if
4. Using try{}catch(){} blocks
5. Designing proper code / testing before production releases
6. To test an array against proper form you could use array_key_exists on a specific key, or test the depth of an array (when it is one !).
7. Always extract your helper methods into the global namespace in a way to reduce duplicate code

Answer 5

Try this:

//Force array
$dataArr = is_array($dataArr) ? $dataArr : array($dataArr);
foreach ($dataArr as $val) {
  echo $val;
}

;)

Answer 6

All answers provided above are essentially just error suppression.

Your PHP is telling you that you are trying to use a variable of incorrect type, and there is possibly an error. but all answers provided are just brushing this message off.

Your best bet is to initialize every variable before use. And to make return types strict and explicit. You must ask yourself, WHY get_values() is returning anything than array? Why it cannot be made to return just an empty array, if no data found? Surely it can be.

Answer 7

foreach ($arr ?: [] as $elem) {
    // Do something
}

This doesen't check if it is an array, but skips the loop if the variable is null or an empty array.

Update from PHP 7.0 you should use the null coalescing operator:

foreach ($arr ?? [] as $elem) {
    // Do something
}

This would solve the warning mentioned in the comment (here a handy table that compares ?: and ?? outputs).

Answer 8

$values = get_values();

foreach ((array) $values as $value){
  ...
}

Problem is always null and Casting is in fact the cleaning solution.

Answer 9

If you're using php7 and you want to handle only undefined errors this is the cleanest IMHO

$array = [1,2,3,4];
foreach ( $array ?? [] as $item ) {
  echo $item;
}

Answer 10

As of PHP >= 7.1.0 use is_iterable

https://www.php.net/manual/en/function.is-iterable.php

if (is_iterable($value)) {
    foreach ($value as $v) {
        ...
    }
}

Answer 11

Warning invalid argument supplied for foreach() display tweets. go to /wp-content/plugins/display-tweets-php. Then insert this code on line number 591, It will run perfectly.

if (is_array($tweets)) {
    foreach ($tweets as $tweet) 
    {
        ...
    }
}

Answer 12

More concise extension of @Kris's code

function secure_iterable($var)
{
    return is_iterable($var) ? $var : array();
}

foreach (secure_iterable($values) as $value)
{
     //do stuff...
}

especially for using inside template code

<?php foreach (secure_iterable($values) as $value): ?>
    ...
<?php endforeach; ?>

Answer 13

There seems also to be a relation to the environment:

I had that "invalid argument supplied foreach()" error only in the dev environment, but not in prod (I am working on the server, not localhost).

Despite the error a var_dump indicated that the array was well there (in both cases app and dev).

The if (is_array($array)) around the foreach ($array as $subarray) solved the problem.

Sorry, that I cannot explain the cause, but as it took me a while to figure a solution I thought of better sharing this as an observation.

Answer 14

Exceptional case for this notice occurs if you set array to null inside foreach loop

if (is_array($values))
{
    foreach ($values as $value)
    {
        $values = null;//WARNING!!!
    }
}

Answer 15

This warning is happening because the array that you want use is empty, you can use of below condition:

if ($your_array != false){
   foreach ($your_array as $value){
         echo $value['your_value_name'];
    }
}

Answer 16

I'll use a combination of empty, isset and is_array as

$array = ['dog', 'cat', 'lion'];

if (!empty($array) && isset($array) && is_array($array) {
    //loop
    foreach ($array as $values) {
        echo $values; 
    }
}

Answer 17

Use is_array function, when you will pass array to foreach loop.

if (is_array($your_variable)) {
  foreach ($your_variable as $item) {
   //your code
}
}

Answer 18

How about this solution:

$type = gettype($your_iteratable);
$types = array(
    'array',
    'object'
);

if (in_array($type, $types)) {
    // foreach code comes here
}

Answer 19

What about defining an empty array as fallback if get_value() is empty?
I can't think of a shortest way.

$values = get_values() ?: [];

foreach ($values as $value){
  ...
}

Answer 20

<?php
 if (isset($_POST['checkbox'])) {
    $checkbox = $_POST['checkbox'];
    foreach ($checkbox as $key) {
       echo $key . '<br>';
    }
}

?>
    <input type="checkbox" name="checkbox[]" value="red">red <br>
    <input type="checkbox" name="checkbox[]" value="green">green <br>