std::cin loops even if I call ignore() and clear()

Question

I\'m trying to setup an input checking loop so it continuously ask the user for a valid (integer) input, but it seems to get trapped in an infinite loop.

I\'ve searched

Answer 1

The ignore() has no effect when the stream is in fail state, so do the clear() first.

Answer 2

When the stream is in an state of error,

  cin.ignore();

does not do anything. You need to call cin.clear() first before calling cin.ignore().

Also, cin.ignore() will ignore just one character. To ignore a line of input, use:

cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

Add

#include <limits>

to be able to use std::numeric_limits.

The fixed up block of code will look something like:

int num;
while ( !(cin >> num) ) {
   cin.clear();
   cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
   cout << "Enter valid number: " << endl;
}