13.3

2019-11-11 05:32:22

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13.29

swap(lhs.ps, rhs.ps);swap(lhs.i, rhs.i);

他们调用的是另一个版本的swap而不是 swap(Hasptr&, HasPtr&) 所以并不会递归

13.30

#include <string>#include <iostream>class HasPtr {public: friend void swap(HasPtr&, HasPtr&); HasPtr(const std::string &s = std::string()) : ps(new std::string(s)), i(0) { } HasPtr(const HasPtr &hp) : ps(new std::string(*hp.ps)), i(hp.i) { } HasPtr& Operator=(const HasPtr &hp) { auto new_p = new std::string(*hp.ps); delete ps; ps = new_p; i = hp.i; return *this; } ~HasPtr() { delete ps; } void show() { std::cout << *ps << std::endl; }PRivate: std::string *ps; int i;};inlinevoid swap(HasPtr& lhs, HasPtr& rhs){ using std::swap; swap(lhs.ps, rhs.ps); swap(lhs.i, rhs.i); std::cout << "call swap(HasPtr& lhs, HasPtr& rhs)" << std::endl;}

13.31

#include <string>#include <iostream>class HasPtr {public: friend void swap(HasPtr&, HasPtr&); friend bool operator<(const HasPtr &lhs, const HasPtr &rhs); HasPtr(const std::string &s = std::string()) : ps(new std::string(s)), i(0) { } HasPtr(const HasPtr &hp) : ps(new std::string(*hp.ps)), i(hp.i) { } HasPtr& operator=(HasPtr tmp) { this->swap(tmp); return *this; } ~HasPtr() { delete ps; } void swap(HasPtr &rhs) { using std::swap; swap(ps, rhs.ps); swap(i, rhs.i); std::cout << "call swap(HasPtr &rhs)" << std::endl; } void show() const { std::cout << *ps << std::endl; }private: std::string *ps; int i;};void swap(HasPtr& lhs, HasPtr& rhs){ lhs.swap(rhs);}bool operator<(const HasPtr &lhs, const HasPtr &rhs){ return *lhs.ps < *rhs.ps;}

13.32 不会类指针并没有分配内存的操作，所以并不会受益

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