Reading CHMOD like values with php

Question

#   Permission
7   read and write and execute (1+2+4)
6   read and write (2+4)
5   read and execute (1+4)
4   read only 
3   write and execute (1+2)
2   write only
1   execute only 
0   none

I like the pattern that you can store any combination of the options options in one integer number, and add options by doubling the last number (8, 16 ,32 etc). I'd like to use this method, and I'd like to know if there's a name for it, and what is the fastest simplest method for turning numbers into results similar to this?

array(1=>false,2=>true,4=>true);//6
array(1=>true,2=>true,4=>true,8=>true);//15

Relevant rant: http://stackoverflow.com/questions/224799/bitwise-flags-abandoned — Ignacio Vazquez-Abrams, Feb 16 '11 at 05:25

Jacob · Accepted Answer · 2011-02-16T05:31:18.440

Using bitwise operations as recommended. To get the array you are after.

This function will figure out the number of bit required for any value given and return the array in the format you suggested.

I've included a loop for 0 to 20 to verify.

<?php

function getBitArray($value) {
    $numberOfBits = ceil(log($value + 1, 2));
    $result = array();
    $bit = 1;
    for($i = 0; $i < $numberOfBits; $i++) {
        $result[$bit] = ($value & $bit) == $bit;
        $bit <<= 1;
    }
    return $result;
}

for($i = 0; $i < 20; $i++)
    var_dump(getBitArray($i));

score 1 · Answer 2 · answered Feb 16 '11 at 05:20

1

That's generally referred to as a bit field, and you can work with it using bitwise operators.

answered Feb 16 '11 at 05:20

Amber

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score 0 · Answer 3 · answered Feb 16 '11 at 05:22

0

This method is known as bitwise operation, and is used in php like this. Here is a nice tutorial.

answered Feb 16 '11 at 05:22

simon

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Reading CHMOD like values with php

3 Answers3