Converting a hex string to a byte array

Question

What is the best way to convert a variable length hex string e.g. \"01A1\" to a byte array containing that data.

i.e converting this:

st         


        

Answer 1

Somebody mentioned using sscanf to do this, but didn't say how. This is how. It's useful because it also works in ancient versions of C and C++ and even most versions of embedded C or C++ for microcontrollers.

When converted to bytes, the hex-string in this example resolves to the ASCII text "Hello there!" which is then printed.

#include 
int main ()
{
    char hexdata[] = "48656c6c6f20746865726521";
    char bytedata[20]{};
    for(int j = 0; j < sizeof(hexdata) / 2; j++) {
        sscanf(hexdata + j * 2, "%02hhX", bytedata + j);
    }
    printf ("%s -> %s\n", hexdata, bytedata);
    return 0;
}