basic_istream::readsome

readsome readsome(E *s, streamsize n);

The member function extracts up to n elements and stores them in the array beginning at s. If rdbuf() is a null pointer, the function calls setstate(failbit). Otherwise, it assigns the value of rdbuf()-<in_avail() to N. if N < 0, the function calls setstate(eofbit). Otherwise, it replaces the value stored in N with the smaller of n and N, then calls read(s, N). In any case, the function returns gcount().