Resetting the State of a Stream

Question

I have a question which is slightly similar to this question on stackoverflow std::cin.clear() fails to restore input stream in a good state, but the answer provided there d

Answer 1

The code here

std::cin.clear(std::istream::failbit);

doesn't actually clear the failbit, it replaces the current state of the stream with failbit.

To clear all the bits, just call clear().

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The description in the standard is a bit convoluted, stated as the result of other functions

void clear(iostate state = goodbit);

Postcondition: If rdbuf()!=0 then state == rdstate(); otherwise rdstate()==(state | ios_base::badbit).

Which basically means that the next call to rdstate() will return the value passed to clear(). Except when there are some other problems, in which case you might get a badbit as well.

Also, goodbit actually isn't a bit at all, but has the value zero to clear out all the other bits.

To clear just the one specific bit, you can use this call

cin.clear(cin.rdstate() & ~ios::failbit);

However, if you clear one flag and others remain, you still cannot read from the stream. So this use is rather limited.