//strvec.cc#include <string> #include <iostream> #include <memory> #include "strvec.h" using namespace std;//一個類對象是const的，它的元素不是const的 StrVec::StrVec(const StrVec &rhs) { //allocate_n_copy:可以開辟新的存儲空間，然后把給定參數范圍的元素逐個拷貝進去，然后 //返回構造好的空間的首元素地址和尾后元素的地址 pair<string*, string*> data = allocate_n_copy(rhs.elements,rhs.first_free); elements = data.first; first_free = cap = data.second; } StrVec& StrVec::operator=(const StrVec & rhs) {auto data = allocate_n_copy(rhs.begin(),rhs.end());free(); //拷貝賦值運算符比拷貝構造函數多一個釋放左側對象的空間的函數elements = data.first;first_free = cap = data.second;return *this; } size_t StrVec::capacity()const {return cap - elements; } size_t StrVec::size()const {return first_free - elements; }void StrVec::free() { if(elements){for(string * p = first_free; p != elements;){alloc.destroy(-- p); }alloc.deallocate(elements,cap - elements); //cap -elements 可以計算一共有多少空間} }void StrVec::chk_n_alloc() { //如果容器已滿，那么重新分配 if(size() == capacity())reallocate(); }pair<string*,string*> StrVec::allocate_n_copy(const string* b,const string * e) {string * const data = alloc.allocate(e - b);return {data,uninitialized_copy(b,e,data)};} allocator<string> StrVec::alloc;void StrVec::reallocate_1() { size_t new_capacity = size() ? 1 : 2 * size(); auto new_elements = alloc.allocate(new_capacity); auto new_first_free = uninitialized_copy(elements,first_free,new_elements); free(); auto new_cap = new_elements + new_capacity; elements = new_elements; first_free = new_first_free; cap = new_cap; }void StrVec::reallocate() {auto new_capacity = size() ? 2*size() : 1; auto new_elements = alloc.allocate(new_capacity); auto dest = new_elements; auto elem = elements; for(int i = 0; i != size() ; ++ i) {//std::move(),在需要構造的地方也是可以使用的 alloc.construct(dest ++,std::move(*elem++)); } free(); elements = new_elements; first_free = dest; cap = new_elements + new_capacity;}void StrVec::push_back(const string & rhs) {chk_n_alloc(); //確保有空間容納新元素alloc.construct(first_free ++,10,'c');}void StrVec::pop_back() {alloc.destroy(first_free --); }StrVec::~StrVec() {free(); }string * StrVec::begin()const {return elements; } string * StrVec::end()const {return first_free; }void StrVec::reserve(size_t s) { if(s <= size()) return ;//先移動元素，然后再釋放左側對象空間 auto const new_elements = alloc.allocate(s); auto dest = new_elements; auto elem = elements; for(size_t i = 0; i != size();++ i ) {alloc.construct(dest ++, std::move(*elem ++));} free(); elements = new_elements; cap = new_elements + s; first_free = dest;}void StrVec::resize(size_t t) { if(t > capacity())return ; else if(t < size()){auto new_first_free = first_free;for(size_t i = 0; i != size() - t; ++ i){alloc.destroy(-- new_first_free);}first_free = new_first_free;return;} else if(t == size()){return ;} else if(t > size()){auto new_first_free = first_free;for(size_t i = 0;i != t - size() ; ++ i){alloc.construct(new_first_free ++,""); } first_free = new_first_free; return;} }void StrVec::print_info()const { cout << "capacity:" << capacity() << endl; cout << "size:" <<size()<< endl; }

文件main.cc

#include <string> #include <iostream> #include <memory> #include "strvec.h" using namespace std; int main() { StrVec v; //cout << v.capacity() << endl; //cout << v.size() << endl;for(int i = 0;i != 10; ++i){v.push_back(string("abcde"));cout << v.size() << endl;} cout <<"capacity:" << v.capacity() << endl; cout <<"size:" << v.size() << endl;for(string * p = v.begin(); p != v.end(); ++p)cout << *p << endl; v.print_info();v.resize(5); v.resize(5); v.resize(100); cout << "big" << endl; v.print_info(); v.reserve(100); v.print_info(); cout << "after resize: " << endl; for(string* p = v.begin(); p != v.end(); ++ p)cout << *p << endl; v.print_info();return 0; } //strvec.h #include <string> #include <iostream> #include <memory> using namespace std; class StrVec {public:StrVec(): //allocator成員進行默認初始化elements(nullptr),first_free(nullptr),cap(nullptr){}StrVec(const StrVec &); //拷貝構造函數StrVec& operator=(const StrVec &);~StrVec();void push_back(const string &);void pop_back();size_t size()const;size_t capacity()const;string *begin()const;string *end()const;//習題13.39void resize(size_t );void reserve(size_t );void shrink_to_fit();void print_info()const;private:static allocator<string> alloc;string *elements; //指向指向數組首元素的指針string *first_free; //指向第一個空閑元素的指針string *cap; //指向數組尾后位置的指針void free(); //銷毀元素并且釋放內存void reallocate_1(); 獲得更多內存并拷貝已有元素void reallocate();pair<string*,string*> allocate_n_copy(const string*,const string*);//開辟空間，拷貝給定范圍的元素void chk_n_alloc();};

運行結果：?

1 2 3 4 5 6 7 8 9 10 capacity:16 size:10 cccccccccc cccccccccc cccccccccc cccccccccc cccccccccc cccccccccc cccccccccc cccccccccc cccccccccc cccccccccc capacity:16 size:10 big capacity:16 size:5 capacity:100 size:5 after resize: cccccccccc cccccccccc cccccccccc cccccccccc cccccccccc capacity:100 size:5

strvec.h中雖然申明了shrink_to_fit，但是這個函數目前實現不了，因為allocator對象分配的空間，目前不能釋放一部分；因為釋放allocator對象分配的空間需要函數deallocate函數，這個函數形如:

deallocate(p,n);其中p必須是先前調用allocate得到的指針，而且n必須是先前調用allocate時候的空間的大小。

所以只能全部釋放呀。不能部分釋放。所以shrink_to_fit是不能實現的。

習題13.40自編答案

StrVec::StrVec(initializer_list<string> li) { //迭代器可以直接給指針賦值，棒呀，都什么情況可以這樣操作呢？ auto data = allocate_n_copy(li.begin(),li.end()); elements = data.first; first_free = cap = data.second; }

練習13.42

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