php serialize empty associative array

Question

I want to dump an associative array to file with php. Sometimes the result can be empty and in this case I want the content of the file be exactly : { } so that I can process all files in the same way. However I can only initialize a simple array in php and so the output in the file is always this : [ ]. I already tried adding a dummy entry to the associative array and then deleting the entry again so that the array is empty, but then again [ ] is the output in the file.

Answer 1

Cast it to object before encoding:

json_encode((object) $array);

Answer 2

Your going to have to check if the array is empty.

if (empty($array_to_dump)) {
    print ':{}';
} else {
    print serialize($array_to_dump);
}

However, the array you get back when you unserialize should be exactly the same either way... an empty array.

Edit: or use the above, even better.

Answer 3

The json_encode function has an option that will coerce arrays into objects where ever contextually appropriate - i.e. associative arrays but this also includes empty arrays, for example:

$array = array(
    'foo' => array(),
    'bar' => array()
);

echo json_encode($array, JSON_FORCE_OBJECT);  // {"foo":{},"bar":{}}

Answer 4

Another answer to this is to use ArrayObject instead of [] when initialising the variable.

The following illustrates the problem. When the associative array is empty, it is JSON encoded as '[]':

$object = [];
echo json_encode($object); // you get '[]'

$object['hello'] = 'world';
echo json_encode($object); // you get '{hello: "world"}'

Instead, keep everything the same, but when you declare the $object, use ArrayObject:

$object = new ArrayObject;
echo json_encode($object); // you get '{}'

$object['hello'] = 'world';
echo json_encode($object); // you get '{hello: "world"}'

The reason this is a good alternative is because using (object) [] converts the variable to an stdClass meaning you have to access the properties using $variable->property. However, if all your existing code was written using $variable['property'], then using (object) [] means you will have to change all of that code, when you can instead just use new ArrayObject.

Link to ArrayObject that has been available since PHP5