How I fixed PHP json_encode() returning empty result

If you are building a RESTful API in PHP, then you are most likely using the json_encode function. json_encode is a PHP function that converts an array to JSON format.

In this article, I will discuss how you can fix a json_encode function that returns an empty result or throws an error.

Debugging the error

The first step in solving a problem is to first know what the problem really is.

First, let’s see if there is any error from json_encode. Add the below code in your code after the json_encode() function that you have:

echo json_last_error_msg(); // Print out the error if any
die(); // halt the script

If what was printed out is — “No errors”, then there is nothing wrong with the data.

Here is the list of errors you might encounter:

https://secure.php.net/manual/en/function.json-last-error.php#refsect1-function.json-last-error-examples

Fixing “Malformed UTF-8 characters, possibly incorrectly encoded” error

This is one of the common error you will face especially if you are fetching your data from a database.

I encountered this error personally which prompted me to write this article. I was working with a result which I fetched from the database that I converted to JSON. Below is my complete code:

$courses = [];
 $db = new mysqli(HOST, USERNAME, PASSWORD, DATABASE);
 if ($db->connect_error) {
     echo (json_encode([
           'status' => 'error',
           'message' => 'connection to database failed.'
     ]));
     die();
 }
 
 if (isset($_GET['count'])) {
      $allCoursesQuery = "SELECT * FROM `courses`";
      $result = $db->query($allCoursesQuery);
      
      echo json_encode(['count' => $result->num_rows]);
      die();
 }
$allCoursesQuery = "SELECT id, title FROM `courses`";
$result = $db->query($allCoursesQuery);
 
 if ($result->num_rows > 0) {
  while ($row = $result->fetch_assoc()) {
   $courses[] = [
                'id' => $row['id'],
                'title' => $row['title']
   ];
  }
 }
 
echo( json_encode([
   'status' => 'success',
   'data' => $courses
]) );
die();

In the code above, I’m fetching all the courses that are in the courses table that is about 164 records. In the last part of the code, I encode the array of courses to JSON then print out the result.

The result was empty, nothing was printed out. But if I LIMIT the result to like 100 records, I get the JSON printed out but any record I fetch above 100 shows empty.

At first, I thought it might be a memory issue (but 164 records is not that much 😕). I went ahead to increase my memory limit but that did not help. It was not memory related.

After much trial and error, I decided to see what json_encode is complaining about if any. So I placed the code after the json_encode(…) function:

echo json_last_error_msg(); // Print out the error if any
die(); // halt the script

Now, I see the error!:

Malformed UTF-8 characters, possibly incorrectly encoded

This error happens if the result contains mixed encoding characters.

To fix it, I introduced JSON_UNESCAPED_UNICODE:

echo( json_encode([
   'status' => 'success',
   'data' => $courses
], JSON_UNESCAPED_UNICODE) );

Conclusion

In this article, you have learned how to debug common json_encode() error and how to get them fixed. Although we did not discuss how to fix all of the errors independently, I strongly believe you can take it from there as you have known what the error message.