Question

I have a C++ console application that takes input from user by displaying a menu and then acting on it. Everything works fine when the user inputs integer values but when the user inputs a ‘?‘ (which I wanted to handle as a ‘display help’ option) the code starts looping infinitely and does not block on the std::cin>> call. Is this expected? What am I missing here?

int queryAction()
{
  while(1) {
    char selection;
    std::cout << "Action: ";
    std::cin >> selection;

    switch(selection)
    {
      //Some code that acts on the selection
      ...
    }
  }
}

Follow Up:
If I add std::cin.clear() before the call to cin>> all is good. I guess my follow up question is why is an error state set on input that should be a valid ascii character?

Answer 1

You never check whether reading was successful. A fundamental part of any programming is proper error handling. std::cin >> selection; will fail if a char cannot be read from the stream or set the eofbit if the end of the source is reached.

A simple way to check this is to use something like the following:

if (!(std::cin >> selection)) // Check if operation failed
{
    std::cout << "Failed to read!\n"; // Notify user
    std::cin.clear(); // Reset stream
    // Ignore rest of line
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}