ゼロ単列c++primer(13)から

      class StrVec{
        public :
            StrVec : elements(nullptr) , first_free(nullptr) , cap(nullptr) { }
            StrVec(const StrVec&);
            ~StrVec();
            void push_back(const std::string&);
            size_t size() const {return first_free - elements;}
            size_t capacity() const {return cap - elements;}
            std::string *begin() const {return elements;} 
            std::string *end() const {renturn first_free;}
        private : 
            static std::allocator<std::string> alloc;
            void chk_n_alloc() {if (size() == capacity()) reallocate();}
            std::pair<std::string*, std::string*> alloc_n_copy(const std::string* , const std::string*);
            void free();
            void reallocate();
            std::string *elements;
            std::string *first_free;
            std::string *cap;
            };