c++ - Read uint8_t from std::stringstream as a numeric type

Question

My understanding is that reading a uint8_t from a stringstream is a problem because the stringstream will interpret the uint8_t as a char. I would like to know how I can read a uint8_t from a stringstream as a numeric type. For instance, the following code:

#include <iostream>
#include <sstream>

using namespace std;

int main()
{
    uint8_t ui;
    std::stringstream ss("46");
    ss >> ui;
    cout << unsigned(ui);
    return 0;
}

prints out 52. I would like it to print out 46.

EDIT: An alternative would to just read a string from the stringstream and then convert the solution to uint8_t, but this breaks the nice chaining properties. For example, in the actual code I have to write, I often need something like this:

   void foobar(std::istream & istream){
       uint8_t a,b,c;
       istream >> a >> b >> c;
       // TODO...
   }

Answer 1

You can overload the input operator>> for uint8_t, such as:

std::stringstream& operator>>(std::stringstream& str, uint8_t& num) {
   uint16_t temp;
   str >> temp;
   /* constexpr */ auto max = std::numeric_limits<uint8_t>::max();
   num = std::min(temp, (uint16_t)max);
   if (temp > max) str.setstate(std::ios::failbit);
   return str;
}

Live demo: https://wandbox.org/permlink/cVjLXJk11Gigf5QE

To say the truth I am not sure whether such a solution is problem-free. Someone more experienced might clarify.

---

UPDATE

Note that this solution is not generally applicable to std::basic_istream (as well as it's instance std::istream), since there is an overloaded operator>> for unsigned char: [istream.extractors]. The behavior will then depend on how uint8_t is implemented.