how can i remove a bit flag in PHP int?

Question

let's say i have

$flags=JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE;

how can i then remove JSON_UNESCAPED_SLASHES from $flags ?

Rather than posting your own answer in the question body, split your question into both a question and own answer. If there are better alternatives around, those can then still be added and upvoted by others. — k0pernikus, Sep 04 '19 at 11:57
When writing a question, there is even a checkbox "Add your own answer" — k0pernikus, Sep 04 '19 at 11:58
See also [operators.bitwise](https://www.php.net/manual/en/language.operators.bitwise.php) — Adder, Sep 04 '19 at 11:59
@vivek_23 you can find the documentation for all of those flags at https://www.php.net/manual/en/json.constants.php - `JSON_PRETTY_PRINT` tries to make the output look "pretty", JSON_UNESCAPED_SLASHES makes it not escape slashes (by default `/` is escaped as `\/`, which is not required by JSON, but php does it anyway, which can optionally be turned off), `JSON_UNESCAPED_UNICODE` makes it add unicode characters in strings literally instead of adding a unicode escape character looking like \uXXXX) — hanshenrik, Sep 04 '19 at 12:06
`$flags` contains several bits of information in one number. — Adder, Sep 04 '19 at 12:06

Robert · Accepted Answer · 2019-09-04T12:03:19.677

5

It's not "C method" it's just applying bitwise operators

$flags=JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE;

var_dump($flags & JSON_UNESCAPED_SLASHES); // flag should be set to 1

$flags &= ~JSON_UNESCAPED_SLASHES; // remove it  

var_dump($flags & JSON_UNESCAPED_SLASHES); // flag should be set to 0

edited Sep 04 '19 at 12:03

answered Sep 04 '19 at 11:59

Robert

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your "should be" comments are wrong. `$flags` is an `int` not a boolean – Adder Sep 04 '19 at 12:01
yeah, maybe I put it wrong in terms of gramma, what I meant is that the flag is either 1 or 0 which evaluates to true, false. I corrected that – Robert Sep 04 '19 at 12:02
Yup, it is true-ish or false-ish. It is zero or not zero, `1` is wrong too. – Adder Sep 04 '19 at 12:03
it isn't. Bitwise it's 1 or 0 :) – Robert Sep 04 '19 at 20:29

score 3 · Answer 2 · answered Sep 04 '19 at 11:59

3

using the C method

$flags &= ~JSON_UNESCAPED_SLASHES;

seems to work.

answered Sep 04 '19 at 11:59

hanshenrik

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How about `$flags ^= JSON_UNESCAPED_SLASHES;` ? – nice_dev Sep 04 '19 at 12:14
2

`$flags ^= JSON_UNESCAPED_SLASHES;` only works when you know that the flag is currently set, but `$flags &= ~JSON_UNESCAPED_SLASHES;` works always to unset the flag. – Adder Sep 04 '19 at 12:19
@Adder Thanks. From the OP, it looked as if it was set already. – nice_dev Sep 04 '19 at 12:21
@vivek_23 `^` is xor which means it toggles the flag. If it was 1 it becomes 0 if it was 0 it becomes 1. – Robert Sep 04 '19 at 12:48
@Robert yes, just realized that. Thanks. Looking at the OP, I presumed it was already set. – nice_dev Sep 04 '19 at 13:03

score 0 · Answer 3 · answered Apr 25 '20 at 10:32

In case you can't reach flags directly, as their are added later in 3rd party code (my case):

<?php

function notMyFunction($flags)
{
    $finalFlags = $flags | FLAG_I_DONT_WANT;
    // ...
}

There is this trick:

<?php


notMyFunction(FLAG_I_DONT_WANT - 1);

how can i remove a bit flag in PHP int?

3 Answers3