Method underflow

test/value.cpp:50–61

{
protected:
    int_type
    underflow() override
    {
        // make sure we don't throw before the parser had the chance to start
        if( !gptr()  )
        {
            setg(buf_, buf_, buf_ + 1);
            return *buf_;
        }

        throw std::invalid_argument("this buffer throws");
    }

private:
    char buf_[1] = {'t'};