cin >> unsigned --> program hang

[Duthomhas]

Hey, I was playing with input the other day with my GCC 4.7, and found the following to produce an unexpected HANG when a negative number was provided at input:

unsigned n;
cin >> n;

(I validated that the problem occurred with stringstream as well, but did not play with a filestream.)

I considered this to be a serious security issue, and was concerned that it happened at all. I mean, I would have presumed that the standard library code would be able to, at the very least, return a nonsense value and leave cin in a fail state. But instead the program just hung, and the standard MS "searching for solution" dialogue came up.


And now that I want to play with it some more, I cannot reproduce the error.


In (supposedly) unrelated news, I am finally happy that I got Microsoft's compiler installed on my machine! (For years I couldn't, because my XP system was one of the few that, for reasons MS couldn't (or wouldn't) explain, refused to successfully install .NET 3.5 -- a known bug for some small number of XP systems). In any case, now that I'm running Windows 7 I've got VS happily installed.

I don't know how MinGW does string-to-integer conversions -- if it is with some MS lib then I may have inadvertently updated it with my fresh VS 11 install...


In any case, has anyone else had this issue? Is this something I should worry about in the FAQ dealing with converting strings to integers? (Remember, I'm being pragmatic with the FAQ, and not idealistic. For example, I'll not claim that <regex> works nicely.)

[Peter87]

If you can't reproduce the error it was probably not what was wrong in the first place. Probably something else in the original program caused the program to hang.

[Duthomhas]

I'm not a newb.

The original program:

#include <iostream>
using namespace std;

int main()
  {
  unsigned n;

  cout << "n? ";
  cin >> n;
  cout << "n = " << n << endl;

  return 0;
  }

[Daleth]

I use MinGW, GCC 4.7 (but with Code::Blocks as my IDE), and your program converted a negative int input to its equivalent unsigned value. cin didn't go into a fail state nor did I get an error you described.

Maybe it was a hiccup from installing a new compiler? Like having to run a new engine for a few minutes to get the oil flowing? I don't have a clue.