I'm developing a WordPress plugin, but the last changes caused the plugin to stop working. It tells me that I can't activate the plugin because it caused a fatal error. On localhost all is working fine, but after sending to the server, on activation it displays the following:

Can't use function return value in write context in /data/web/virtuals/72282/virtual/www/wp-content/plugins/wp-songbook/inc/wpsongs-shortcs.php on line 83

I really don't understand the context of this message, because the code of this line is:


Can anyone tell me what's happened?

closed as off-topic by Mark Kaplun, Pieter Goosen, birgire, gmazzap, Johannes Pille Sep 15 '14 at 18:11

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Your question should be specific to WordPress. Generic PHP/JS/HTML/CSS questions might be better asked at Stack Overflow or another appropriate site of the Stack Exchange network. Third party plugins and themes are off topic." – Mark Kaplun, Pieter Goosen, birgire, gmazzap, Johannes Pille
If this question can be reworded to fit the rules in the help center, please edit the question.


The root of the problem is that isset expects a variable to be passed to it. Also, I'm assuming that you expect the get_post_meta() to return a scalar value and not an array, so I added the third parameter set to true.

// 3rd param: $single. Value of true means get scalar value, not an array.    
$ytlink = get_post_meta( get_the_ID(), 'songbook_video_link', true );

// Will ensure that $ytlink is boolean false, and not an empty string.
$ytlink = ( ! empty( $ytlink ) ) ? $ytlink : false;
  • Sorry, Ive tried to use your code, and got this message (only on domain): The plugin generated 573 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin. – user1980807 Sep 14 '14 at 11:12
  • No Problem. That code snippet does not generate any output, so it's not the culprit. Can you please post your code? – Dave Romsey Sep 14 '14 at 18:49
  • I explored, that the trouble was by wrong activation hook function, that returned something... Thank you for help :) – user1980807 Sep 15 '14 at 17:21

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