13.2.1

2019-11-14 10:40:27

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13.23 有一定差异，我使用if判断是否自我拷贝本节使用先拷贝右侧对象的方式来使自我拷贝正常运行

13.24 如果没有定义析构函数，肯定会发生内存泄露如果没有定义拷贝构造函数，当使用了拷贝构造函数时，删除一个对象会使和其他对象共用的内存被释放，其他对象则出现错误

13.25 拷贝构造和拷贝赋值必须新建内存，而不是和右侧共用内存

当shared_ptr计时器为0时，会自动的释放，所以不需要析构函数

13.26 @pezy

https://github.com/PYPARA/Cpp-PRimer/blob/master/ch13/ex13_26.h

#include <vector>#include <string>#include <initializer_list>#include <memory>#include <exception>using std::vector; using std::string;class ConstStrBlobPtr;class StrBlob {public: using size_type = vector<string>::size_type; friend class ConstStrBlobPtr; ConstStrBlobPtr begin() const; ConstStrBlobPtr end() const; StrBlob():data(std::make_shared<vector<string>>()) { } StrBlob(std::initializer_list<string> il):data(std::make_shared<vector<string>>(il)) { } // copy constructor StrBlob(const StrBlob& sb) : data(std::make_shared<vector<string>>(*sb.data)) { } // copyassignment Operators StrBlob& operator=(const StrBlob& sb); size_type size() const { return data->size(); } bool empty() const { return data->empty(); } void push_back(const string &t) { data->push_back(t); } void pop_back() { check(0, "pop_back on empty StrBlob"); data->pop_back(); } std::string& front() { check(0, "front on empty StrBlob"); return data->front(); } std::string& back() { check(0, "back on empty StrBlob"); return data->back(); } const std::string& front() const { check(0, "front on empty StrBlob"); return data->front(); } const std::string& back() const { check(0, "back on empty StrBlob"); return data->back(); }private: void check(size_type i, const string &msg) const { if (i >= data->size()) throw std::out_of_range(msg); }private: std::shared_ptr<vector<string>> data;};class ConstStrBlobPtr {public: ConstStrBlobPtr():curr(0) { } ConstStrBlobPtr(const StrBlob &a, size_t sz = 0):wptr(a.data), curr(sz) { } // should add const bool operator!=(ConstStrBlobPtr& p) { return p.curr != curr; } const string& deref() const { // return value should add const auto p = check(curr, "dereference past end"); return (*p)[curr]; } ConstStrBlobPtr& incr() { check(curr, "increment past end of StrBlobPtr"); ++curr; return *this; }private: std::shared_ptr<vector<string>> check(size_t i, const string &msg) const { auto ret = wptr.lock(); if (!ret) throw std::runtime_error("unbound StrBlobPtr"); if (i >= ret->size()) throw std::out_of_range(msg); return ret; } std::weak_ptr<vector<string>> wptr; size_t curr;};ConstStrBlobPtr StrBlob::begin() const // should add const{ return ConstStrBlobPtr(*this);}ConstStrBlobPtr StrBlob::end() const // should add const{ return ConstStrBlobPtr(*this, data->size());}StrBlob& StrBlob::operator=(const StrBlob& sb){ data = std::make_shared<vector<string>>(*sb.data); return *this;}int main(){ return 0;}

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