Converting string to binary and back to string is not the same with PHP

Question

I came up with the PHP code below which converts a binary string 00000010 to the string "representation" and then later I convert it back to the binary string, however it's not getting back the same original binary string 00000010. The code below works perfectly with 10000010, 11000010... but for some strange reason it does not work with 00000010. Why?

$binary = '00000010';
echo $binary . "\n";

$temp = pack('H*',dechex(bindec($binary)));
echo str_pad(decbin(ord($temp)),8,'0',STR_PAD_LEFT);

OUTPUT:

00000010
00100000

I know some string "representation" of some binary strings are not visible/printable chars, but I dont care printing those chars. I just want to convert it to that string "representation" and back, but it's not working. What I am doing wrong?

EDIT:

After great help of @Rocket Hazmat the code started working for some binaries but not for others. The code below, for example, does not look to work, it outputs 0 instead of 10101010.

$binary = '10101010';
$temp = pack('C',base_convert($binary,2,16));
echo base_convert(ord($temp),16,2);

gen_Eric · Accepted Answer · 2020-11-02 18:57:40Z

1

Using pack() with h* (or h) is what you want here. You are reading it in as a hex value (after converting from binary), so you want pack to see it as a hex value.

$temp = pack('h', base_convert($binary, 2, 16));

The problem was when you convert it back. ord returns you a base 10 number. I was incorrectly converting it as a hex (base 16) value:

base_convert(ord($temp), 10, 2)

Though, after looking at the code again, I think you don't even need pack() here. You are using ord(), so we can use its opposite, chr():

$temp = chr(base_convert($binary, 2, 10));

chr() wants a (base 10) int though, not a hex value, so let's use that.

What seems to be working is the following:

$temp = chr(base_convert($binary, 2, 10));
echo str_pad(base_convert(ord($temp), 10, 2), 8, '0', STR_PAD_LEFT);

edited Nov 2, 2020 at 18:57

answered Nov 2, 2020 at 18:22

gen_Eric

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12 Comments

Samul Over a year ago

So how do I create a code that knows when to use H and h? Because you are right, using h* solves the problem to convert 00000010 go and back, but it breaks all the other binary string that I tried with H*! BTW, thanks for pointing about the * :)

gen_Eric Over a year ago

@Samul: I see the issue. Instead of h or H, you actually want C. And you can simplify the dechex/bindec/dechex using base_convert. I'll update the answer.

Samul Over a year ago

Worked perfectly my friend, you nailed it! Thanks for not only posting the code, your comments were very valuable!

Samul Over a year ago

My friend, I tried your most recent code with the string 10101010 and it does not work, it returns 0. Maybe I am doing something wrong?

gen_Eric Over a year ago

@Samul I am working on it. I think I see what I did wrong.

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