Question

I wrote this simple code:

 #include <iostream>
 using namespace std;
 int main()
 {
   double s;
   cin >> s;
   if (cin.fail())
     cout<<"Error";
   return 0;
 }

When I enter 12.03, cin.fail() returns false, and that’s good.

And when I enter sd234, cin.fail() returns true, which is also good.

But if I enter 234.abcd, for example, or any number followed by a characters, cin.fail() returns true although I didn’t enter a numerical to the double variable through the cin.

What am I missing?

Answer 1

std::istream::operator>>() reads characters as long as it fits to the current type (e.g. digits and . for double). Following characters are left in the input buffer for another extraction operator. If the characters read can satisfy the current type, no error is signaled.