ESP8266 Community Forum

Posted: **Wed Feb 10, 2016 1:08 pm**

I want to use the WakeOnLAN example posted at https://github.com/mikispag/arduino-Wak ... eOnLan.ino It accepts a byte array for the input like this: byte pc_mac[] = {0x00, 0x24, 0x1D, 0xCD, 0x6D, 0x24}

I've made a webserver where the user can type in the target, which gets stored as a String, like this: 00241dcd6d24

Now I'm a newbie when it comes to C so this might be an easy one for a real programmer, but I'm having a devil of a time figuring out how to turn that user typed string into the byte[] that the function can use. Can anybody throw me a bone? I appreciate it.

Posted: **Fri Feb 12, 2016 2:52 pm**

Never let a thread die unanswered!

At some point I realized that I was asking the question in the wrong way. What I should have been asking myself is "How do you change an ASCII HEX value into an *actual* HEX value?" Once I started down that path I ended up with the following, which works, with a little help from Google.

Code: Select all

int HexDigit(byte c)
{
   if (c >= '0' && c <= '9') {
       return c - '0';
   } else if (c >= 'a' && c <= 'f') {
       return c - 'a' + 10;
   } else if (c >= 'A' && c <= 'F') {
       return c - 'A' + 10;
   } else {
       return -1;   // getting here is bad: it means the character was invalid
   }
}

int Hexify(char y, char z)
{
   byte a = HexDigit(y);
   byte b = HexDigit(z);
   if (a<0 || b<0) {
       return -1;  // an invalid hex character was encountered
   } else {
       return (a*16) + b;
   }
}

pc_mac[0] = Hexify(myString.charAt(0), myString.charAt(1));
pc_mac[1] = Hexify(myString.charAt(2), myString.charAt(3));
pc_mac[2] = Hexify(myString.charAt(4), myString.charAt(5));
pc_mac[3] = Hexify(myString.charAt(6), myString.charAt(7));
pc_mac[4] = Hexify(myString.charAt(8), myString.charAt(9));
pc_mac[5] = Hexify(myString.charAt(10), myString.charAt(11));

I'm sure that could be prettier, but heck I've got 4M to fill up.

ESP8266 Community Forum

Need assistance converting String to byte array

Need assistance converting String to byte array

Re: Need assistance converting String to byte array