iostream doesn't know it's at the end of the file until it tries to read that first character past the end of the file.
The sample code at cplusplus.com says to do it like this: (But you shouldn't actually do it this way)
while (is.good()) // loop while extraction from file is possible
{
c = is.get(); // get character from file
if (is.good())
cout << c;
}
A better idiom is to move the read into the loop condition, like so:
(You can do this with all istream read operations that return *this, including the >> operator)
char c;
while(is.get(c))
cout << c;