PHP: Check if Key is equal to string

Question

I'm working with a two-dimensional array, and as I'm iterating through each index of this array, I'm trying to check if the current key is equal to a string.

Here's how I'm trying to do it:

foreach($_POST['items'] as $index => $item){

    $key = key($item);

    if($key == 'image'){
        echo 'hello';
    }

}

This throws the error Invalid argument supplied for foreach()

How do you check if the current key is equal to a particular string?

var_dump

array(2) { 
    [0]=> array(1) { ["paragraph"]=> string(4) "paragraph 1" } 
    [1]=> array(1) { ["paragraph"]=> string(4) "paragraph 2" } 
} 
array(2) { 
    [0]=> array(1) { ["paragraph"]=> string(4) "paragraph 3" } 
    [1]=> array(1) { ["paragraph"]=> string(4) "paragraph 4" } 
}

Here is the element within the form with name image:

<div><input type="file" name="items[][image]" id="uploadImage" multiple></div>

var_dump of dynamic form with 1 image input followed by 1 paragraph input

array(1) { 
    [0]=> array(1) { ["paragraph"]=> string(11) "paragraph 1" } 
}

var_dump is not seeing the input with name image???

Here is the form Its contents are dynamically added from <script>

<form method="post" action="insert.php" enctype="multipart/form-data">

        <textarea name="title"></textarea>

        <input type="submit" name="upload" value="Upload" id="upload">
    </form>

One of the dynamic adding functions (this one is for image inputs)

    function addImage() {
    $("form").append('<div><input type="file" name="items[][image]" id="uploadImage" multiple></div>');
}

That error means $_POST['items'] is not something you can loop through with foreach. Your first step should be to make sure it's actually an array. — rickdenhaan
– rickdenhaan, Commented Jul 14, 2017 at 23:10
What is the contents of the $_POST['items'] variable? -- If you have not performed any processing on it then it is likely a String, and not an array. — Drefetr
– Drefetr, Commented Jul 14, 2017 at 23:11
I don't see how removing that if would have any bearing on the "Invalid argument supplied for foreach". — Don't Panic
– Don't Panic, Commented Jul 14, 2017 at 23:13
It doesn't change during the loop, so there's no need to do the same thing every time. But it doesn't matter. I tried to reproduce your error, I couldn't. — Barmar
– Barmar, Commented Jul 14, 2017 at 23:21
But if you're getting that error, you shouldn't get into the foreach loop at all. Are you sure the error is coming from this code? The error message should have a line number on it. — Barmar
– Barmar, Commented Jul 14, 2017 at 23:22

Kevin P · Accepted Answer · 2017-07-14 23:13:06Z

1

Check if $_POST['items'] is an array

if(is_array($_POST['items'])){
    foreach($_POST['items'] as $index => $item){

        $key = key($item);

        if($key == 'image'){
            echo 'hello';
        }
    }
}

answered Jul 14, 2017 at 23:13

Kevin P

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3 Comments

rpivovar Over a year ago

Thanks, I didn't know about is_array. Without the if statement there are no errors.

rpivovar Over a year ago

Is the usage of is_array for testing purposes, or would you always use it when dealing with arrays?

localheinz Over a year ago

@coffeebot You would use is_array() when you want to find out if a value is an array, context doesn't matter. For reference, see php.net/manual/en/function.is-array.php.

slevy1 · Accepted Answer · 2017-07-15 00:50:40Z

Another way is to use array_walk_recursive() which nicely takes care of the iteration for you; it is done implicitly and it's fast, too. So, if $_POST["items"] were similar to the following array, this example code shows how to test for an element whose key is "key":

<?php

$arr = ["1" => "a",
        "2" => "b",
        "3" => [10 => "apple",
                11 => "cat", 
                12 => ["key" => "image" ]]];

if ( array_walk_recursive($arr, function($item,$key) {

     if ($key == "key") {
           echo "\nKey is $key and item is $item";
      }


})) { echo "\narray_walk_recursive rocks :)";  }

See live code.

The built-in function array_walk() saves the coder from also having to check whether an element represents an array or a scalar value since the function possesses that kind of detection. The only thing that is required is to design the callback function, which in this case is an anonymous function.

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