basic_istream::unget

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basic_istream::unget

basic_istream& unget();

The unformatted input function puts back the previous element in the stream, if possible, as if by calling rdbuf()->sungetc(). If rdbuf() is a null pointer, or if the call to sungetc returns T::eof(), the function calls setstate(badbit). In any case, it returns *this.