Istream input checking - c++

Question

I have function, which recieves coeffecents of polynomial via istream input. Im struggling with implementing this piece of code into it (can't fully understand how istream& works), so i can shield it from incorrect input. :
while (!std::cin.good())
{
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
std::cout << "error";
std::cin >> A;
}
Into the function itself:
std::istream& operator>>(std::istream& s, Polynom& c)
{
for (int i = 0; i <= c.degree; i++)
s >> c.coefficents[i];
return s;
}
Needless to say, that's how it is implemented in main()
std::cin >> A;
Polynom class:
class Polynom
{
private:
int degree;
double* coefficents;
public:
Polynom();
Polynom(int size);
Polynom(const Polynom&);
~Polynom();
int get_degree();
double get_coefficents(int);
Polynom operator+(const Polynom&);
Polynom operator-(const Polynom&);
Polynom operator*(double p);
void operator=(const Polynom&);
friend std::ostream& operator<< (std::ostream& s, const Polynom& c);
friend std::istream& operator>> (std::istream& s, Polynom& c);
double& operator()(int i)
{
return coefficents[i];
}
};
Any hints or optimal solutions are welcomed :)

Answer 1

Expanding my comment to an answer, it's possible to make a function which takes the stream and uses the read-validation loop inside it to get the value.
Then in your operator>> overload you call this function to get each value.
Perhaps something like this:
template<typename T>
bool get_value(std::istream& input, T& value)
{
while (!(input >> value))
{
// If end of file, don't attempt any more validation
if (input.eof())
{
return false;
}
// Clear the error
input.clear();
// Ignore the rest of the line
input.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
// When the loop ends, we have successfully read a value from the stream
// Return true to tell that
return true;
}
You could use it as:
std::istream& operator>>(std::istream& s, Polynom& c)
{
double value;
for (int i = 0; i <= c.degree && get_value(s, value); i++)
c.coefficents[i] = value;
return s;
}