Convert null in json_encode to empty strings?

Question

I am having trouble trying to convert null values to empty strings with the results of my json_encode:

    if ($uresult->num_rows >0) {


 while($urow = $uresult->fetch_assoc()) {


 $rresult = mysqli_query($con,"SELECT * FROM allid WHERE postid='$oldid' AND spaceid='$newid'");
 $lrow = mysqli_fetch_assoc($rresult);
 $tem = $lrow['postid'];

 $ujson = json_encode($tem);
 echo $ujson;
 }

} else {
}

Here is the result of the $ujson:

"10"nullnullnullnull"25"

I looked up answers and I got this answer:

array_walk($tem,function(&$item){$item=strval($item);});

Doing this caused me to get this error:

Warning: array_walk() expects parameter 1 to be array, string given

Is this the correct way to convert a null to an empty string, if so, what am I doing wrong?

it already says string given, it means $tem is a string

Kevin
– Kevin

2018-06-01 01:18:15 +00:00
Commented Jun 1, 2018 at 1:18 — Kevin
– Kevin, Commented Jun 1, 2018 at 1:18

Rohit Suthar · Accepted Answer · 2020-07-28 18:34:53Z

4

Try this way -

//Array
$array = ["id" => 1, "name" => "Rohit Suthar", "city" => null, "mobile" => null];

//Convert null value to empty string 
array_walk_recursive($array,function(&$item){$item=strval($item);});

echo json_encode($array);

answered Jul 28, 2020 at 18:34

Rohit Suthar

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Comments

Kevin · Accepted Answer · 2018-06-01 01:42:17Z

3

Like what I've said in the comments, it says $tem is a string. array_walk needs an array for it to work properly.

Anyway, if you intend null values to turn into empty string '', just array_map with strval the array you got, so that it applies strval each element in the array. Then finally, encode it.

Here's the general idea:

$lrow = array_map('strval', $lrow);

Looking more in depth, you should put all items inside a container first, and then finally encode them. Don't encode each batch. Regarding the $tem's, then you wouldn't need array_walk, just a ternary operator:

$post_ids = array();
if ($uresult->num_rows > 0) {
    while ($urow = $uresult->fetch_assoc()) {
        $rresult = mysqli_query($con,"SELECT * FROM allid WHERE postid='$oldid' AND spaceid='$newid'");
        $lrow = mysqli_fetch_assoc($rresult);
        $tem = !is_null($lrow['postid']) ? $lrow['postid'] : '';
        $post_ids[] = $tem;
    }
}

echo json_encode($post_ids);

Sidenote: As much as possible, avoid using a while loop, and inside it another query under it (imagine having a thousand rows; it will query a thousand times too). Use JOIN statements instead.

edited Jun 1, 2018 at 1:42

answered Jun 1, 2018 at 1:20

Kevin

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6 Comments

Laney Williams Over a year ago

Ok I did this and got this error: array_map(): Argument #2 should be an array

Kevin Over a year ago

@LaneyWilliams you apply it into an array, anyways, just check out the edit, it should show you in the right direction

Kevin Over a year ago

@Darren looking at the question as a whole, i think the OP doesn't need an array_walk or array_map at all.

Darren Over a year ago

@Ghost Just did haha, it's early here and I haven't had my coffee yet. Your edit sums up nicely ;-)

Kevin Over a year ago

@Darren coffee works wonders, my brain never work without it. :D

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