How to convert a binary string to array?

Question

For example I have an integer

$mask = 210;

which in binary is

$binary = decbin($mask); // "11010010"

Now I want to convert this ($mask or $binary) to an array with the indexes which is true:

$expected = [2, 5, 7, 8];

What is the best way to do this?

Split `$binary` to an array, push a 0 to give yourself offsets from 1 rather than from zero, reverse it, filter to remove falsey values, and get the keys — Mark Baker, Dec 22 '15 at 08:10
@u_mulder only str_split came to my mind and then use foreach to loop the chars array to push the indexes to an new array if the value is "1", but I guess this would not be efficient, comparing to bitwise operations... — Phoenix, Dec 22 '15 at 08:13
@Phoenix I assume you are trying to create a bitmask for permission storage. If that's not the case, please update the question with your intended goal and I'll vote to reopen. — Gordon, Dec 22 '15 at 08:17

Yeldar Kurmangaliyev · Answer 1 · 2015-12-22T08:15:53.690

1

You can do this manually:

$expected = array();

$mask = 210;
$binary = strrev(decbin($mask)); // strrev reverts the string

for ($i = 0; $i < strlen($binary); $i++)
{
    if ($binary[$i] === '1') $expected[] = ($i + 1);
}

Working IDEOne demo.

Important note: bits are usually being numerated from zero. So, the correct answer would be "1 4 6 7". Change ($i + 1) to $i in order to achieve this result.

edited Dec 22 '15 at 08:15

answered Dec 22 '15 at 08:10

Yeldar Kurmangaliyev

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score 0 · Answer 2 · answered Dec 22 '15 at 08:16

Split $binary to an array, push a 0 to give yourself offsets from 1 rather than from zero, reverse it, filter to remove falsey values, and get the keys

$mask = 210;
$binary = decbin($mask); // "11010010"

$tmp = str_split($binary, 1);
$tmp[] = 0;
$expected = array_keys(
    array_filter(
        array_reverse($tmp)
    )
);

var_dump($expected);

Demo

How to convert a binary string to array?

2 Answers2