Hi~ I'm Anka!

What will happen#

If the content of test.txt cannot be parsed as an integer (e.g. "abc"):

1. The extraction fails
   • fileStream >> x fails to read an int.
2. The stream enters a failure state
   • The failbit is set.
3. x remains unchanged
   • Since x is uninitialized, its value is undefined (this is a bug).
4. Further reads from the stream will also fail
   • Until the error state is cleared.

How to fix the program#

1
std::ifstream fileStream("test.txt");
2
if (!fileStream) {
3
    std::cerr << "Failed to open file\n";
4
    return;
5
}

1
int x = 0;

1
int x = 0;
2
if (fileStream >> x) {
3
    std::cout << "Read value: " << x << '\n';
4
} else {
5
    std::cerr << "File does not contain a valid integer\n";
6
}

1
fileStream.clear();              // clear failbit
2
fileStream.ignore(std::numeric_limits<std::streamsize>::max(), '\n');