php - Undefined offset: 3 in custom function

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I am using this code as part of a function:

function photo_shortcode($atts){
   extract(shortcode_atts(array(
      'no' => 1,
   ), $atts));

   $no     = is_numeric($no) ? (int) $no : 1;
   $images = get_field('fl_gallery');
   $image  = $images[$no];
}

fl_gallery is an ACF gallery field. However, sometimes I am getting PHP Notice: Undefined offset: 1,2,3 etc.. on line $image = $images[$no];

Why would this be happening and how to fix it?

I am using this code as part of a function:

function photo_shortcode($atts){
   extract(shortcode_atts(array(
      'no' => 1,
   ), $atts));

   $no     = is_numeric($no) ? (int) $no : 1;
   $images = get_field('fl_gallery');
   $image  = $images[$no];
}

fl_gallery is an ACF gallery field. However, sometimes I am getting PHP Notice: Undefined offset: 1,2,3 etc.. on line $image = $images[$no];

Why would this be happening and how to fix it?

• php
• functions

Share Improve this question edited Jul 31, 2020 at 10:07 JoaMika asked Jul 31, 2020 at 10:05 JoaMikaJoaMika 69866 gold badges2727 silver badges5858 bronze badges 4

• What is $no? And what does the value of $images look like? – Jacob Peattie Commented Jul 31, 2020 at 10:07
• Hi I have updated the code, $no is an integer which corresponds to which object to pick from the array $images – JoaMika Commented Jul 31, 2020 at 10:09
• I suppose the error might be happening if you call the shortcode with [photo no="3"] but there are only 2 images in the fl_gallery ? – JoaMika Commented Jul 31, 2020 at 10:14
• You shouldn't use extract, I also see your shortcode doesn't return anything, and you never check if get_field worked or not, you're just assuming it worked. What if there is n gallery? Or yoour shortcode runs before a post is set as the current post? Or on a 404 page? Clearly it didn't work and the code just carried on anyway, resulting in the PHP notices – Tom J Nowell ♦ Commented Jul 31, 2020 at 10:21

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1 Answer 1

Sorted by: Reset to default 1

You assumed get_field would always return images, but what if there are no images to return?

   $images = get_field('fl_gallery');
   $image  = $images[$no];

The code never checks $images to see if it's empty, or an error value.

On top of that, what if it returned images, but it returned 3 images, and $no is 4? You can't access something that doesn't exist without warnings, you have to check first. This is why you're getting PHP warnings.

For example:

if ( empty( $images ) ) {
    // no images!
}

if ( empty( $images[$no] ) ) {
    // that image doesn't exist
}

However, you're using get_field which is an ACF API, not a WordPress API. You will need to consult the ACF documentation on what that function does when it encounters problems, and how to handle the error. It may not return an array at all but final HTML.

You'll also want to add more validation. For example [photo_shortcode no=9000] or [photo_shortcodo no="-1"] or [photo_shortcode no="0.5"] are all numeric and would generate those PHP warnings

Sidenote: extract reduces security, makes code unreadable by machines and tools, and can overwrite variables unexpectedly enabling security holes and bugs. Never use it.

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