#include <iostream>
#include <string>
#include <algorithm>
#include <stdexcept>
std::string string_to_hex(const std::string& input)
{
static const char* const lut = "0123456789ABCDEF";
size_t len = input.length();
std::string output;
output.reserve(2 * len);
for (size_t i = 0; i < len; ++i)
{
const unsigned char c = input[i];
output.push_back(lut[c >> 4]);
output.push_back(lut[c & 15]);
}
return output;
}
std::string hex_to_string(const std::string& input)
{
static const char* const lut = "0123456789ABCDEF";
size_t len = input.length();
if (len & 1) throw std::invalid_argument("odd length");
std::string output;
output.reserve(len / 2);
for (size_t i = 0; i < len; i += 2)
{
char a = input[i];
const char* p = std::lower_bound(lut, lut + 16, a);
if (*p != a) throw std::invalid_argument("not a hex digit");
char b = input[i + 1];
const char* q = std::lower_bound(lut, lut + 16, b);
if (*q != b) throw std::invalid_argument("not a hex digit");
output.push_back(((p - lut) << 4) | (q - lut));
}
return output;
}
using namespace std;
int main () {
string str1 = "Hello";
string hexstr = string_to_hex(str1);
cout << "string input:" << str1 << endl << "Hexa out:"<< hexstr <<endl;
cout<< "string out:"<<hex_to_string(hexstr);
return 0;
}
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