stringstream runs into infinite loop

[manasij7479]

using namespace std;
class token
{
    public:
    bool status;//0 for str & 1 for num
    string str;
    double num;
} ;
typedef vector<token> storage;

int main()
{
    string a;
    token t;
    storage s;
    double x;
    string y;
    getline(cin,a);
    istringstream st;
    st.str(a);
    while(!st.eof())
    {
        if(st>>x,x)
        {
            
            t.status=true;
            t.num=x;
            cout<<t.num<<'\n';

        }
        else
        {
            st>>y;
            t.status=false;
            t.str=y;
            cout<<t.str<<'\n';

        }
        //cout<<t.status;
        s.push_back(t);
    }

}

The number part executes nicely but whenever I put strings into the input....the while starts an infinite loop.
btw_ this is for parsing the input for a calculator program...
Any idea what is going wrong...or a better way to put the different parts of the input line to be analysed separately later?

[hamsterman]

when >> fails you have to .clear() the stream and every operation will fail until you do that.

[manasij7479]

then the stream would start right at the beginning again and would never meet the .eof() condition of the loop.Is there a way to take it back through one operation ...which I could use in the beginning of the else block?... seems that the >> is used twice every time a string is encountered.

[hamsterman]

Are you sure? The http://www.cplusplus.com/reference/iostream/ios/clear/ seems not to mention reseting the get pointer.
By the way, what is st >> x,x supposed to do?

[manasij7479]

I was wrong about that....recently learnt that it would only clear the last read....in this case ,the error of trying to read a string into a double...
st >>x,x first reads x from the stream and then turns up a true condition if it is double...and a false if it is a string..

[hamsterman]

and what do you thing st >> x would do?

[manasij7479]

read x from the input stream until a whitespace is encountered

[filipe]

And what does st >> x return?

[manasij7479]

When an expression has a , within it, the left part is evaluated but doesn't return anything...the condition of the if block comes from the nature of x.

[hamsterman]

operator >> returns a reference to istream object which is convertible to a boolean. When an error occurs, This bool = false. Your code gets input and then checks if that input is 0.
Try compiling this:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

#include <iostream> #include <limits> int main(){ double i; while(true){ if(std::cin >> i, i){ std::cout << "y" << i << "\n"; }else{ std::cout << "n" << i << "\n"; std::cin.clear(); std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); } } return 0;

Input: 0 Output: n0 Input: string Output: n0 Input: 5 Output y5 Input: string Output: endless loop of "y5"