getint.cpp

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#include <iostream>
#include <climits> // for INT_MAX

/***
 * If the istream is in a "failed" state due to malformed input, resets the
 * stream to a "good" state and ignores the line containing the malformed
 * input so that the caller can retry the input. Does nothing if the istream
 * is in a "good" state or if the failure is due to something other than
 * malformed input (e.g., EOF), from which the stream cannot recover.
 *
 * @return true if input failed but can be retried; false otherwise
 ***/
bool retry (std::istream &in) {
  if (in.rdstate() != in.failbit) return false;
  in.clear();
  return in.ignore(INT_MAX, '\n');
}

int main () {
  using namespace std;

  int i;

  cout << "Enter an int: ";
  while (retry(cin >> i)) cout << "That wasn't an int. Try again: ";

  if (cin) { // got input
    cout << "You entered " << i << '\n';
  }

  else { // didn't get input
    cout << "You didn't enter anything!\n";
  }

  return 0;
}