How to convert Hex to binary in PHP?

Question

I'm trying to send 0x01 HEX as Byte using the socket_write($socket, XXXX , 1); function.

There is part of documentation:

"...If yes, server will reply to module 0x01, if not – replay 0x00. Server must send answer – 1 Byte in HEX format."

I have tried this: $data = pack('H*', "0x01"); socket_write($socket, $data , 1); ...but it's not working. — Enid
– Enid, Commented Oct 22, 2014 at 18:19

mario · Accepted Answer · 2014-10-22 18:27:01Z

12

There are multiple alternatives:

When using the pack() function, the string argument to the H* format specifier should not include the 0x prefix.
```
pack("H*", "01")
```
To convert a single hex-number into a byte you can also use chr().
```
chr(0x01)
```
Here PHP first interprets the hex-literal 0x01 into a plain integer 1, while chr() converts it into a string. The reversal (for socket reading) is ord().
The most prevalent alternative is using just using C-string escapes:
```
"\x01"
```
Or in octal notation:
```
"\001"
```
hex2bin("01") works just like pack("H*") here. And there's bin2hex for the opposite direction.

answered Oct 22, 2014 at 18:27

mario

146k20 gold badges243 silver badges293 bronze badges

Sign up to request clarification or add additional context in comments.

1 Answer 1