Question

Let’s suppose I have a string str which consists of characters default to hexadecimal system (0-9, a-f):

string str="1234567890abcdef";

I also have an empty array of n-length (n is known):

unsigned char arr[n] 

What I would like to do is fill my array arr with values of str but in a specific manner shown below:

unsigned char arr[8] = {0x12U, 0x34U, 0x56U, 0x78U, 0x90U, 0xabU, 0xcdU, 0xefU};

As it is presented the string str was divided into smaller hexadecimal chars. How can I achieve it? The algorithm for seperation is simple, but I can’t figure out how to change string to unsigned char and how to add 0x at the beginning and U at the end of the chars.

Answer 1

Your requirements are somewhat unclear. Does the following program perform the action you desire?

#include <string>
#include <iostream>
#include <cstdio>
#include <iterator>
#include <algorithm>


void str2bin(const std::string& in, unsigned char out[])
{

    const char* data = in.data();
    const std::string::size_type size = in.size();
    for(std::string::size_type i = 0; i < size; i+= 2) {
        unsigned int tmp;
        std::sscanf(data+i, "%02X", &tmp);
        out[i/2] = tmp;
    }
}

int main() {
    unsigned char arr[8];
    str2bin("1234567890abcdef", arr);
    std::cout << std::hex;
    std::copy(arr, arr+8, std::ostream_iterator<unsigned int>(std::cout, ", "));
    std::cout << "\n";
}