16.12编写你自己版本的Blob和BlobPtr模板，包含书中未定义的多个const成员。
Blob.h(注意，成员函数的声明和定义要放在一个头文件中）
/*记住，模板的头文件中通常既包括声明也包括定义。函数模板和类模板成员函数的定义通常放在头文件中，不能分开放。。。。谨记*/ #ifndef BLOB_H #define BLOB_H #include<iostream> #include<vector> #include<string> #include<memory> #include<initializer_list> using namespace std; template <typename> class BlobPtr; template <typename> class Blob; template <typename T> bool operator==(const Blob<T>&,const Blob<T>&); template <typename T> class Blob { friend class BlobPtr<T>; friend bool operator==<T> (const Blob<T>&,const Blob<T>&); public: typedef T value_type; typedef typename vector<T>::size_type size_type; Blob(); Blob(initializer_list<T> il); BlobPtr<T> begin() { return *this;} BlobPtr<T> end() { auto ret=BlobPtr<T>(*this,this->size()); return ret;} size_type size() const { return data->size();} bool empty() const { return data->empty();} void push_back(const T &t) { data->push_back(t);} void push_back(T &&t) { data->push_back(std::move(t));} void pop_back(); T& front(); T& back(); const T& front() const; const T& back() const; T& operator[](size_type i); const T& operator[](size_type i) const; private: shared_ptr<vector<T>> data; void check(size_type i,const string &msg) const; }; template <typename T> Blob<T>::Blob(): data(std::make_shared<std::vector<T>>()) { } template<typename T> Blob<T>::Blob(initializer_list<T> il):data(make_shared<vector<T>>(il)) {} template<typename T> void Blob<T>::check(size_type i,const string &msg) const { if(i>=data->size()) throw out_of_range(msg); } template<typename T> void Blob<T>::pop_back() { check(0,"pop_back"); data->pop_back(); } template <typename T> T& Blob<T>::front() { check(0,"front"); return data->front(); } template<typename T> T& Blob<T>::back() { check(0,"back"); return data->back(); } template<typename T> const T& Blob<T>::front() const { check(0,"front"); return data->front(); } template<typename T> const T& Blob<T>::back() const { check(0,"back"); return data->back(); } template<typename T> T& Blob<T>::operator[](size_type i) { check(i,"out_of_range"); return (*data)[i]; } template<typename T> const T& Blob<T>::operator[](size_type i) const { check(i,"out_of_range"); return (*data)[i]; } template <typename T> bool operator==(const Blob<T> &lhs,const Blob<T> &rhs) { if(rhs.size()!=lhs.size()) return false; for(size_t i=0;i!=lhs.size();+i) if(lhs[i]!=rhs[i]) return false; return true; } template <typename T> ostream operator<<(ostream &os,const Blob<T> &a) { os<<"<"; for(size_t i=0;i!=a.size();++i) os<<a[i]<<" "; os<<">"; return os; } template <typename T> bool operator==(const BlobPtr<T>&,const BlobPtr<T>&); template <typename T> class BlobPtr { friend bool operator==<T> (const BlobPtr<T>&,const BlobPtr<T>&); public: BlobPtr():curr(0){} BlobPtr(Blob<T> &a,size_t sz=0):wptr(a.data),curr(sz){} T& operator*() const { auto p=check(curr,"dereference past end"); return (*p)[curr]; } BlobPtr& operator++(); BlobPtr& operator--(); BlobPtr& operator++(int); BlobPtr& operator--(int); private: shared_ptr<vector<T>> check(size_t,const string &) const; weak_ptr<vector<T>> wptr; size_t curr; }; template <typename T> shared_ptr<vector<T>> BlobPtr<T>::check(size_t i,const string &msg) const { auto ret=wptr.lock(); if(!ret) throw runtime_error("unbind BlobPtr"); if(i>=ret->size()) throw out_of_range(msg); return ret; } template <typename T> BlobPtr<T>& BlobPtr<T>::operator++() { check(curr,"++"); ++curr; return *this; } template <typename T> BlobPtr<T>& BlobPtr<T>::operator--() { --curr; check(curr,"--"); return *this; } template <typename T> BlobPtr<T>& BlobPtr<T>::operator++(int) { auto ret=*this; ++*this; return ret; } template <typename T> BlobPtr<T>& BlobPtr<T>::operator--(int) { auto ret=*this; --*this; return ret; } template <typename T> bool operator==(const BlobPtr<T> &lhs,const BlobPtr<T> &rhs) { return (lhs.wptr.lock().get()==rhs.wptr.lock().get())&&lhs.curr==rhs.curr; } template <typename T> bool operator!=(const BlobPtr<T> &lhs,const BlobPtr<T> &rhs) { return !(rhs==lhs); } #endif // BLOB_H
main.cpp
#include "Blob.h" int main() { Blob<string> b1; // empty Blob cout << b1.size() << endl; { // new scope Blob<string> b2 = {"a", "an", "the"}; b1 = b2; // b1 and b2 share the same elements b2.push_back("about"); cout << b1.size() << " " << b2.size() << endl; } // b2 is destroyed, but the elements it points to must not be destroyed cout << b1.size() << endl; for(auto p = b1.begin(); p != b1.end(); ++p) cout << *p << endl; return 0; }
16.14 编写Screen类模板，用非类型参数定义Screen的高和宽。
16.15为你的Screen模板实现输入和输出运算符。Screen类需要哪些友元来令输入和输出运算符正确工作。
#include<iostream> #include <string> using namespace std; //模板非类型参数，友元一定要前置声明 template <unsigned H,unsigned W> class Screen; template <unsigned H,unsigned W> ostream& operator<<(ostream &os,const Screen<H,W> &s); template <unsigned H,unsigned W> istream& operator>>(istream &is,Screen<H,W> &s); template <unsigned H,unsigned W> class Screen { friend ostream& operator<< <H,W> (ostream &os,const Screen<H,W> &s); friend istream& operator>> <H,W> (istream &is,Screen<H,W> &s); public: typedef string::size_type pos; Screen()=default; Screen(pos ht,pos wd,char c):height(ht),width(wd),contents(ht*wd,c){} char get() const { return contents[cursor]; } inline char get(pos ht,pos wd) const; Screen &move(pos r,pos c); private: pos cursor=0; pos height=H; pos width=W; string contents; }; template<unsigned H,unsigned W> char Screen<H,W>::get(pos ht,pos wd) const { pos row=ht*width; return contents[row+wd]; } template <unsigned H,unsigned W> Screen<H,W>& Screen<H,W>::move(pos r,pos c) { pos row=r*width; cursor=row+c; return *this; } template <unsigned H,unsigned W> ostream& operator<<(ostream &os,const Screen<H,W> &s) { os<<s.cursor<<" "<<s.height<<" "<<s.width<<" "<<s.contents[s.cursor]<<endl; return os; } template <unsigned H,unsigned W> istream& operator>>(istream &is,Screen<H,W> &s) { is>>s.cursor>>s.height>>s.width>>s.contents; return is; } int main() {}
16.16