Question

I have a character array (an ethernet address like aa:bb:cc:dd:ee:ff) that I need to parse up into an unsigned char[6]. I’m using strtok to get each pair of characters, and I need to cast them into an unsigned char, but nothing I’m doing is working.

I’ve tried (assume c is a char* of length 2):

unsigned char t = (unsigned char)c;  // gives "loses precision" error

unsigned char* t = (unsigned char*)c;
unsigned char t1 = t[0];                  // gives the wrong value

unsigned char t;
strcpy((char*)t, c);      // gives the wrong value
strncpy((char*)t, c, sizeof(char)*2) // gives the wrong value

Answer 1

Assuming that your input string is a hex string containing at most two hexadecimal numbers, i. e. FF you can use std::stringstream to do the conversion:

int n;

std::stringstream ss;
ss << std::hex << c;
ss >> n;

unsigned char x = (unsigned char)n;

You’ll have to ensure, that c really is not bigger than FF.

EDIT: Changed the above code to read the value into an int first and then cast it to unsigned char. When reading directly into a char it’s reading characters only without any conversion.