String Hex to Byte Array

Question

How do I convert a String which has hex values to a byte array that has those hex values? I am using Arduino by the way.

This:

String 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 hex value 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);

Answer 1

I am assuming you need an array of hex values ie array of integers from the String s . Thogh from char test[] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}; , it seems you want a char array. If you add the code below after your code you will get an integer array named hexn which will contain your hex values.

    int i,hexn[20],k=0,j;
    char tmp[8];
    for (i=0;charArray[i]!='\0' ;i++){
        if(charArray[i]=='x' && charArray[i-1]=='0'){
            j=0;
            while(charArray[i]!=','){
                tmp[j++]=charArray[++i];
                if (charArray[i]=='\0')
                    break;
            }
            sscanf(tmp,"%x",&hexn[k++]);
        }
    }

Now if you really need char test[] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}; , I suppose you are not getting the opening and closing braces, ie { and } . in that case you can use the concatenation operator. You can to do something like this before your code,

String s2 = String('{') + s + String('}');

Hope it will help you.