How to solve the problem when converting php array to json format is empty

When we use json_encode() in PHP to convert an array into a JSON string, we sometimes encounter a problem. No matter how we operate, the converted JSON string will be empty. This problem can be frustrating, but its solution is simple.

Locating the problem

First, we need to find the problem. We can use the var_dump() function to view the contents of the array and check if there are any exceptions or the expected data.

For example:

<?php
$arr = array("name" => "John", "age" => 30, "city" => "New York");
var_dump($arr);
echo json_encode($arr);
?>

This code will output the following:

array(3) {
  ["name"]=>
  string(4) "John"
  ["age"]=>
  int(30)
  ["city"]=>
  string(8) "New York"
}

Then, we try to use json_encode() to convert the array into a JSON string. As a result, what we get is an empty string. This result surprised us and made us question our own skill level.

Troubleshooting

Next, let’s troubleshoot the problem step by step.

1. Make sure the array is UTF-8 encoded

PHP’s json_encode() function requires that the input data must be UTF-8 encoded. If there are non-UTF-8 encoded characters in the array, the conversion to a JSON string will fail.

You can convert the strings in the array to UTF-8 encoding through the iconv() or mb_convert_encoding() function. For example:

<?php
$arr = array("name" => "John", "age" => 30, "city" => "New York");
foreach($arr as &$value){
    $value = mb_convert_encoding($value, 'UTF-8', 'auto');
}
echo json_encode($arr);
?>

2. Make sure the array does not contain null values

The JSON specification does not allow the use of null values. Therefore, if the array contains null values, using json_encode() will cause the conversion to fail and return null.

At this time, you can use the array_map() function to replace the null value in the array with an empty string. For example:

<?php
$arr = array("name" => "John", "age" => null, "city" => "New York");
$arr = array_map(function($value){
    return $value !== null ? $value : '';
},$arr);
echo json_encode($arr);
?>

3. Make sure that the key names in the array are valid

The key names in JSON must be of string type, which means that the key names in the array must be is a string. If you are using numbers as keys, you will have problems using the json_encode() function.

In the following example, when we use the json_encode() function, the result is an empty string:

<?php
$arr = array(0=>'apple',1=>'banana',2=>'orange');
echo json_encode($arr);
?>

At this time, you need to change the numeric key name to a string type . For example:

<?php
$arr = array(&#39;0&#39;=>'apple','1'=>'banana','2'=>'orange');
echo json_encode($arr);
?>

4. Make sure there are no infinite loop references in the array

If there are infinite loop references in the array, it will cause the json_encode() function to be unable to process the array, and Returns an empty string. If your array has self-reference relationships nested in it, you will definitely find this problem when using json_encode().

While solving this problem, you need to ensure that your array can be serialized. That is, you should replace all object references with serializable data types. For example:

<?php
$arr = array();
$item1 = array(&#39;id&#39;=>1,'name'=>'apple');
$item2 = array('id'=>2,'name'=>'banana');
$item1['next'] = &$item2;
$item2['prev'] = &$item1;
$item3 = array('id'=>3,'data'=>array_merge($item1,$item2));
$arr[] = $item1;
$arr[] = $item2;
$arr[] = $item3['data'];
echo json_encode($arr);
?>

In this example, we create an array containing a self-referential relationship. In order to solve the problem, we changed the object reference to a serializable data type, which avoided the problem of infinite reference cycles and allowed us to successfully convert the array into a JSON string.

Summary

Don’t panic when you encounter an empty JSON string when using json_encode() in PHP. By following the above four methods, you can easily solve this problem. Please make sure that the array is UTF-8 encoded, that the array does not contain null values, that the key names in the array are valid, and that there are no infinite circular references in the array. You can happily use the json_encode() function to convert your Array successfully converted to JSON string.

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