convert String Hex to Hex byte array

Hello,

My apologies if this is a naive question. How do I convert a String which has hex values to a byte array that has those hex values?

This:

Stirng s = "0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff";

Needs to be converted to this:

 char test[] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff};

I used the following procedure. It does convert it, however, each character is saved as a character as opposed to hex value:

 unsigned int str_len = s.length()+1;
 char charArray[str_len];
 s.toCharArray(charArray, str_len);

Any help will be appreciated. Thank you!

strtol(); set base to 16

1. You have:

Stirng s = "0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff"; //here, there is a difference between f and F
==> Stirng s = {0x30, 0x78, 0x66, 0x66, 0x2C, ..., 0x20, 0x30, 0x78, 0x66, 0x66, 0x00};

2. You want:

byte test[] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};//here, no difference between f and F

In what practical system/processing, you need this kind of transformation?

GolamMostafa:
In what practical system/processing, you need this kind of transformation?

I have an E-ink display that I am trying to update by making HTTP calls from my Arduino nano IoT. This is the value of an image converted to 1 bitmap and then into a byte array and sent over HTTP to my Arduino.