cin not behaving as expected

[dmc]

Hi,
I'm passing cin some erroneous input, but it's not failing as expected. The code is just:

  cout << "Please enter an integer: ";
  int n = 0;
  cin >> n;
  cout << "Got : " << n << "\n";
  if (cin.fail()) cout << "cin was left in failed state.\n";

When I give an input that begins with an integer, but also then contains non-numeric characters, I don't get a failed state, e.g.:

$ ./a.out
Please enter an integer: 44ffffff
Got : 44
$

It's as if it's delimiting on the first non-numeric character it comes across, rather than just whitespace. Can anyone explain why please? I'm using g++ (v4.9.2) under Debian "jessie".

[wizebin]

As far as I remember that is compiler dependent, undefined territory.

In other words don't rely on that functionality even if it does have a consistent behavior. I would expect the results to be inconsistent. (If you want it to work the way you expect you could parse the values from the string and handle your exceptions in whatever way you want)

[jlb]

It's as if it's delimiting on the first non-numeric character it comes across, rather than just whitespace. Can anyone explain why please?

Because that is the way the C++ streams were designed, much like their C-stdio counterparts. The processing of a number will stop when a non-digit is encountered. The only time the stream will fail is if the first character is not either the sign (+-) or a digit. If any valid numeric character is encountered before any invalid character, the stream will be in a "good" state and the remaining characters will be left in the input buffer for further processing.

As far as I remember that is compiler dependent, undefined territory.

No it is well defined and specified by the standard.

[dmc]

Thanks for the clarification.

[wizebin]

No it is well defined and specified by the standard.

Well guess I have beans for memory xD