C++ Primer, Fifth Edition

Copy-Control Members

Given our alloc_n_copy and free members, the copy-control members of our class are straightforward. The copy constructor calls alloc_n_copy:

StrVec::StrVec(const StrVec &s) {     // call alloc_n_copy to allocate exactly as many elements as in s     auto newdata = alloc_n_copy(s.begin(), s.end());     elements = newdata.first;     first_free = cap = newdata.second; }

and assigns the results from that call to the data members. The return value from alloc_n_copy is a pair of pointers. The first pointer points to the first constructed element and the second points just past the last constructed element. Because alloc_n_copy allocates space for exactly as many elements as it is given, cap also points just past the last constructed ...