C++ exception specification for iostream operator overloading

Question

It is not specified if call to ostream operator<< can fail or throw any exception and I have never encounter this.

1. Is there a case where ostream operator<< could fail ?
2. If no, why standard does not put noexcept specifier to these overloads ?
3. Is the following overload valid ? good practice ? commonly used ?
4. Same question for istream operator>> ?

struct MyClass {
    int data;
    // I/O operators with noexcept specifier
    friend std::istream& operator>>(std::istream &in, MyClass &obj) noexcept;
    friend std::ostream& operator<<(std::ostream &out, const MyClass &obj) noexcept;
};

Answer 1

The reason none of the operator >> and operator << are marked as noexcept is because of std::basic_ios::exceptions. This member function is present in all objects that inherit from std::basic_ios and allows you to configure the stream to throw exceptions for certain failure modes. If the operators were noexcept then you could not use them with a stream that has exceptions set.