Question

…and return the number as string.

How can I do that? Is there any library for that?

Answer 1

You can use std::istringstring from <sstream> to convert the strings to integers. Then you can use rand or random to get a random number, which you can constrain to the interval using modular arithmetic, and then you can convert the number to a hexadecimal string using std::ostringstream.

#include <sstream>
#include <string>
#include <cstdlib>

int hexstr2int(const std::string& str)
{
    int result;
    std::istringstream iss(str);
    iss >> result;
    return result;
}

std::string int2hexstr(int number)
{
   std::ostringstream oss;
   oss << std::hex << number;
   return number.str();
}

int randint(int lower, int upper)
{
     int range = upper - lower;
     return ((rand()%range)+lower);
}

std::string randhexstr(const std::string& a, const std::string& b)
{
    int lower = hexstr2int(a);
    int upper = hexstr2int(b);
    return int2hexstr(randint(lower,upper));
}