File read fails with ios_base::failbit - c++

Question

I have a simple C++ file read program:
int main() {
std::string buf;
std::ifstream file;
file.exceptions(std::ifstream::failbit | std::ifstream::badbit);
try {
file.open("C:\\Test11.txt");
char c;
while (!(file.eof())) {
file.get(c);
std::cout << c;
}
}
catch (std::ifstream::failure e) {
std::cout << e.what() << std::endl;
std::cout << e.code() << std::endl;
std::cout << "Exception opening/reading file";
}
file.close();
return 0;
}
The content of file at C:\Test11.txt is Hello.
The program is able to read the content but fails with exception ios_base::failbit. It seems to have problem while evaluating while (!(file.eof())).
What is going wrong?

Answer 1

The issues is that eof() is not true until you attempt to read past the end of file.
So once you have correctly read the whole of the file and there is no data left in the file. The result of eof() is still false (as you have not read past the end). It is the next read that will set eof() but it is also the next read that will fail (and thus throw an exception).
This is why checking for eof() is an anti-pattern.
while (!(file.eof()))
{
file.get(c);
std::cout << c;
}
The better (correct) pattern is:
while (file.get(c)) // reads next character into c returns a ref to file.
// Note: when a stream is used in a boolean context
// such as an while () it is converted to bool
// using !good(). Thus if the read fails
// and the bad bit is set and the loop will exit.
{
std::cout << c;
}