C++ //练习 16.16 将StrVec类（参见13.5节，第465页）重写为模板，命名为Vec。

C++ Primer（第5版） 练习 16.16

练习 16.16 将StrVec类（参见13.5节，第465页）重写为模板，命名为Vec。

环境：Linux Ubuntu（云服务器）

工具：vim

代码块

#include<iostream>
#include<memory>
#include<utility>
using namespace std;

template <typename T> class Vec{
	
    public:
    Vec(): elements(nullptr), first_free(nullptr), cap(nullptr) {}
    Vec(const Vec &);
    Vec &operator= (const Vec &);
    ~Vec();
    void push_back(const T &);
    size_t size() const { return first_free - elements; } 
    size_t capacity() const { return cap - elements; }
    T *begin() const { return elements; }
    T *end() const { return first_free; }
    void reserve(std::size_t s);
    void resize(std::size_t s);

    private:
    Static std::allocator<T> alloc;
    void chk_n_alloc(){ if (size() == capacity()) reallocate(); }
    std::pair<T*, T*>alloc_n_copy(const T*, const T*);
    void free();
    void reallocate();
    T *elements;
    T *first_free;
    T *cap;
};

template <typename T>
void Vec<T>::push_back(const T &s){
    chk_n_alloc();
    alloc.construct(first_free++, s);
}

template <typename T>
std::pair<T*, T*> Vec<T>::alloc_n_copy(const T *b, const T *e){
    auto data = alloc.allocate(e - b);
    return {data, uninitialized_copy(b, e, data)};
}

template <typename T>
void Vec<T>:free(){
    if(elements){
        for(auto p = first_free; p != elements; ){
            alloc.destroy(--p);

        }
        alloc.deallocate(elements, cap - elements);
    }
}

template <typename T>
Vec<T>::Vec(const Vec &s){
    auto newdata = alloc_n_copy(s.begin(), s.end());
    elements = newdata.first;
    first_free = cap = newdata.second;
}

template <typename T>
Vec<T>::~Vec() { free(); }

template <typename T>
Vec<T> &Vec<T>::operator= (const Vec &rhs){
    auto data = alloc_n_copy(rhs.begin(), rhs.end());
    free();
    elements = data.first;
    first_free = cap = data.second;
    return *this;
}

template <typename T>
void Vec<T>::reallocate(){
    auto newcapacity = size() ? 2 * size() : 1;
    auto newdata = alloc.allocate(newcapacity);
    auto dest = newdata;
    auto elem = elements;
    for(size_t i = 0; i != size(); ++i){
        alloc.construct(dest++, move(*elem++));
    }
    free();
    elements = newdata;
    first_free = dest;
    cap = elements + newcapacity;
}

template <typename T>
void Vec<T>::reserve(std::size_t s){
	if(s <= size()){
	 	return;
	}
	auto newElem = alloc.allocate(s);
	auto dest = newElem;
	auto elem = elements;
	for(size_t i = 0; i != size(); ++i){
		alloc.construct(dest++, move(*elem++));
	}
	free();
	elements = newElem;
	cap = newElem + s;
	first_free = dest;
}

template <typename T>
void Vec<T>::resize(std::size_t s){
	if(s > capacity()){
		return ;
	}
	if(s < size()){
		auto newFisrt = first_free;
		for(size_t i = 0; i != size() - s; ++i){
			alloc.destroy(--newFirst);
		}
		fisrt_free = newFirst;
		return ;
	}
	else if(s == size()){
		return ;
	}
	else{
		auto newFirst = first_free;
		for(size_t i = 0; i != s - size(); ++i){
			alloc.construct(newFirst++, "");
		}
		first_free = newFirst;
		return ;
	}
}