from int cast to byte, from byte extract hex values.

charcast.cpp

#include <iostream>

using namespace std;

struct Byte {
	void to4Bits(char c)
	{
		lo = c >> 4;
		hi = c & 0x0F;
	}

	unsigned int lo : 4, hi : 4;
} Byte;

void byteTohex(char c, char hex[2])
{
	static const char hexTable[] = {
		'0', '1', '2', '3',
		'4', '5', '6', '7',
		'8', '9', 'A', 'B',
		'C', 'D', 'E', 'F'
	};
	Byte.to4Bits(c);
	hex[0] = hexTable[Byte.lo];
	hex[1] = hexTable[Byte.hi];
}

int main()
{
	char c[2];
	
	unsigned int h = 0xDEADBEEF;
	char *karr = (char *)&h;

	for (int i = 3; i >= 0; --i) {
		byteTohex(karr[i] , c);
		cout << c;
	}
	
	cout << endl;
	               
	uint64_t w = 0xFADEBED012345678;
	char *warr = (char *)&w;

	for (int i = 7; i >= 0; --i) {
		byteTohex(warr[i] , c);
		cout << c;
	}

	return 0;
}