PHP - How to update JSON data in a txt file?

Question

Here is a JSON data example saved in a file data.txt

   [
     {"name":"yekky"},
     {"name":"mussie"},
     {"name":"jessecasicas"}
     ...// many rows
    ]

I would like to update the file so it will look like this:

[
 {"name":"yekky","num":"1"},
 {"name":"mussie","num":"2"},
 {"name":"jessecasicas","num":"3"}
 ...// many rows
]

This is what I have got so far:

$json_data = file_get_contents('data.txt');
// What goes here?

And how do I count how many rows there are in the JSON tree?

Already answered in php-json-decode-a-txt-file and stackoverflow.com/questions/6311813/… — J.C. Inacio
– J.C. Inacio, Commented Jun 11, 2011 at 0:38
@jcinacio, I am studing json now. So first question is how to write, now is how to update. it is easy for you, but not easy for a student. — fish man
– fish man, Commented Jun 11, 2011 at 0:44
there are exactly 2 json functions in php - json_encode and json_decode. I suggest you to read the PHP manual — J.C. Inacio
– J.C. Inacio, Commented Jun 11, 2011 at 0:46

rid · Accepted Answer · 2011-06-11 00:35:40Z

6

Use json_decode() to decode the JSON data in a PHP array, manipulate the PHP array, then re-encode the data with json_encode().

For example:

$json_data = json_decode(file_get_contents('data.txt'), true);
for ($i = 0, $len = count($json_data); $i < $len; ++$i) {
    $json_data[$i]['num'] = (string) ($i + 1);
}
file_put_contents('data.txt', json_encode($json_data));

answered Jun 11, 2011 at 0:35

rid

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7 Comments

BenMorel Over a year ago

$json_data[$i] is actually an object, not an array. Your code won't work.

rid Over a year ago

@Benjamin Morel, double check the documentation.

BenMorel Over a year ago

@Radu, run your code: Fatal error: Cannot use object of type stdClass as array. His JSON is an array of objects.

rid Over a year ago

@Benjamin Morel, works just fine. You probably forgot to write the , true part on the json_decode() call.

BenMorel Over a year ago

You're right, it does indeed with $assoc = true. Still found it misleading though to convert to a PHP array, then let json_encode() convert that back to a JS object (because the keys are not numeric).

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Community · Accepted Answer · 2017-05-23 12:26:23Z

You should use the PHP JSON library for such tasks. For example, after having read your JSON data from the file, do something like:

$json = json_decode($json_data);
$itemCount = count($json);

After having modified your JSON data, just encode it again:

$json_data = json_encode($json);

Also, you seem to want to beatify your JSON data. My advise is to just use whatever comes out of json_encode and save that to your file, because it will probably be the smallest (in file size) possible representation of your JSON data.

If you format it in a way readable for humans, you've got lots of extra spaces / tabs / line-breaks which increase file size and parsing time.

If you need to read it yourself, you can still beautify your JSON data by hand.

BenMorel · Accepted Answer · 2011-06-11 00:55:20Z

2

$file = 'data.txt';
$data = json_decode(file_get_contents($file));
foreach ($data as $key => $obj) {
    $obj->num = (string)($key+1);
}
file_put_contents($file, json_encode($data));

edited Jun 11, 2011 at 0:55

answered Jun 11, 2011 at 0:37

BenMorel

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