I have some input to be read by a input filestream (for example):

-365.269511 -0.356123 -Inf 0.000000

When I use std::ifstream mystream; to read from the file to some

double d1 = -1, d2 = -1, d3 = -1, d4 = -1;

(assume mystream has already been opened and the file is valid),

mystream >> d1 >> d2 >> d3 >> d4;

mystream is in the fail state. I would expect

std::cout << d1 << " " << d2 << " " << d3 << " " << d4 << std::endl;

to output

-365.269511 -0.356123 -1 -1. I would want it to output -365.269511 -0.356123 -Inf 0 instead.

This set of data was output using C++ streams. Why can't I do the reverse process (read in my output)? How can I get the functionality I seek?

From MooingDuck:

#include <iostream>
#include <limits>

using namespace std;

int main()
{
  double myd = std::numeric_limits<double>::infinity();
  cout << myd << '\n';
  cin >> myd;
  cout << cin.good() << ":" << myd << endl;
  return 0;
}

Input: inf

Output:

inf
0:inf

See also: http://ideone.com/jVvei

Also related to this problem is NaN parsing, even though I do not give examples for it.