Convert a char array to hex binary format C++

Question

I have a string storing 16 hex chars. For example:

const char* arr = "DD2B23B62AC245DA";

I need to write those chars into a binary file in a format of 8 bytes. Each byte is represented by two hex chars in their hex value. The way I did it is:

unsigned char  hexArr[8];
hexArr[0] = 0xDD;
hexArr[1] = 0x2B;
hexArr[2] = 0x23;
...

The problem in that way is that it is hard-coded, and I need to be able to get this array as an input and then to fill the hexArr array.

When I copy the array itself it sets the hex value of the char D instead of D as a hexadecimal value. Any help how can I do that?

Maybe it's not an option for you, but have you considered this format for input instead? http://ideone.com/ayEYsC — Nicolas Louis Guillemot, Mar 27 '14 at 07:25
No, I get it as such a string. May I can edit the string - but the answer I got was easier for me. — user1016179, Mar 27 '14 at 07:28

score 1 · Accepted Answer · answered Mar 27 '14 at 06:59

The easiest way is in my opinion to do the conversion yourself by code:

std::vector<unsigned char> parseHex(const char *s) {
    std::vecotr<unsigned char> result;
    int acc=0, n=0;
    for (int i=0; s[i]; i++) {
        acc <<= 4;
        if (s[i] >= '0' && s[i] <= '9')      acc += (s[i] - '0');
        else if (s[i] >= 'a' && s[i] <= 'f') acc += 10 + (s[i] - 'a');
        else if (s[i] >= 'A' && s[i] <= 'F') acc += 10 + (s[i] - 'A');
        else throw std::runtime_error("invalid hex literal digit");
        if (++n == 2) {
            result.push_back(acc);
            acc = n = 0;
        }
    }
    if (n) throw std::runtime_error("invalid hex literal length");
    return result;
}

score 0 · Answer 2 · answered Mar 27 '14 at 07:51

Though the answer above is accepted, I think this one is more elegant:

int chartoint(char c) {
  const char* buf = "0123456789abcdef";
  const char* ptr = std::strchr(buf, std::tolower(c));

  if (!ptr)
    throw std::runtime_error("Not a hex digit:" + c);
  return ptr - buf;
}

void cast(const char* arr, std::vector<unsigned char>* chvec) {
  size_t arrlen = strlen(arr);
  if (arrlen & 1) {
    throw std::runtime_error(std::string("odd string length:") + arr);
  }

  while (*arr) {
    int val = chartoint(*arr++) << 4;
    val += chartoint(*arr++);
    chvec->push_back(val);
  }
}

Convert a char array to hex binary format C++

2 Answers2

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