What is the recommended (standard) way of handling invalid input in extraction operator:
std::istream& operator>>(std::istream& is, SomeType& val) {
// ...
return is;
}
Should it set std::ios_base::failbit and return immediately? Is it okay to leave the val object in undefined state, with possibly some of it's variables already changed?
According to FormattedInputFunction documentation the recommended layout:
std::istream& operator>>(std::istream& is, SomeType& val) {
std::istream::sentry s(is);
if (s) {
// do parse
if (parsing_failed) {
// optionally, to make it work like built-in operators:
// val = {};
is.setstate(std::ios_base::failbit);
}
}
return is;
}
I would follow the convention of the standard library - that is, set failbit, leave the stream pointing to the same place you started with and set your input to some default value - the standard library sets inputs to 0 on error, so do whatever the logical equivalent of that for your type is, probably val = SomeType{};.