C++Primer 16章·11-20

16.11 List的定义是错误的，应该如何修正？

修改后：

template <typename elemType> class ListItem;
template <typename elemType> class List {
public:
	List();//在List模板内调用List可以省略<>
	List(const List<elemType> &);
	List& operator=(const List<elemType>&);
	~List();
	//ListItem在模板类定义外调用需要加上<>
	void insert(ListItem<elemType>* ptr, elemType value);
private:
	ListItem * front, * end;
};

16.12 编写你自己版本的Blob和BlobPtr，包含书中未定义的多个const

这道题涉及到新学的模板类的定义和模板友元的声明以及之前学到的const类型函数、智能指针、运算符重载等内容。如果跟我一样战线拉得比较长得同学可以试着重写以下这个Blob。如果之前学得比较好的话，可以直接从12章-19题的Strbol.h改成template模板熟悉一下模板的声明。程序如下：

blob.h

#ifndef BLOB_H
#define BLOB_H

#include<vector>
#include<string>
#include<memory>
#include<initializer_list>
using namespace std;

template <typename t> class blobptr;
template <typename T> bool operator==(const blobptr<T>&, const blobptr<T>&);

template<typename T> class blob {
	friend class blobptr<T>;
public:
	blob();
	blob(initializer_list<T> il);//接受{}列表初始化

	string::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(const T&& t) { data->push_back(t); }
	void pop_back();
	T& front();
	const T& front()const;
	T& back();
	const T& back()const;
	T& operator[](string::size_type i);
	const T& operator[](string::size_type i) const;
	//与书上不同，改为了const版本，
	//同时blobptr构造函数的接受参数也要改为const版本的引用
	blobptr<T> begin() const {return  blobptr<T>(*this);}
	blobptr<T> end() const {return blobptr<T>(*this,data->size());}
private:
	shared_ptr<vector<T>> data;
	void check(string::size_type i,const string& s)const;//检查溢出
};

template<typename T> blob<T>::blob() : data(make_shared<vector<T>>()){}
template<typename T> blob<T>::blob(initializer_list<T> il): 
	data(make_shared<vector<T>>(il)){}
template<typename T> void blob<T>::pop_back() {
	check(0, "no elem here");
	return data->pop_back();
}
template<typename T> T& blob<T>::back() {
	check(0, "no elem here");
	return data->back();
}
template<typename T> const T& blob<T>::back()const {
	check(0, "no elem here");
	return data->back();
}
template<typename T> T& blob<T>::front() {
	check(0, "no elem here");
	return data->front();
}
template<typename T> const T& blob<T>::front()const {
	check(0, "no elem here");
	return data->front();
}
template<typename T> T& blob<T>::operator[](string::size_type i) {
	check(i, "out of range");
	return (*data)[i];
}
template<typename T> const T& blob<T>::operator[](string::size_type i)const {
	check(i, "out of range");
	return (*data)[i];
}
template<typename T> 
void blob<T>::check(string::size_type i, const string& s)const {
	if (i >= data->size())
		throw out_of_range(s);
}

//blobptr相当于一个blob的迭代器
template <typename t> class blobptr {
	friend bool operator==<t>(const blobptr<t>& lhr, const blobptr<t>& rhr);
public:
	blobptr():curr(0){}
	blobptr( const blob<t> &pb ,const size_t sz = 0):wptr(pb.data),curr(sz){}
	t & operator*() const;
	blobptr & operator++();

private:
	shared_ptr<vector<t>>  check(const size_t sz,string msg) const;
	weak_ptr<vector<t>> wptr;
	size_t curr;
};
template <typename t>
shared_ptr<vector<t>> blobptr<t>::check(const size_t sz,string msg)const {
	auto ret = wptr.lock();
	if(!ret)
		throw runtime_error("unbond");
	else if(sz >= ret->size())
		throw out_of_range(msg);
	return ret;
}
template <typename t>
t & blobptr<t>::operator*()const{
	auto pb = check(curr,"out of range");
	return (*pb)[curr];
}
template <typename t>
blobptr<t> & blobptr<t>::operator++(){
	check(curr,"the end");
	++curr;
	return *this;
}

template <typename T> 
bool operator==(const blobptr<T>& lhr, const blobptr<T>& rhr) {
	return (lhr.curr == rhr.curr );
}

#endif // !BLOB_H

main.cpp

#include<iostream>
#include<string>
#include"blob.h"

using namespace std;

int main(int argc, char** argv) {
	//测试 blob 功能(int)
	cout << "普通版本功能测试" << endl;
	blob<int> a = {1,2,3,4,5,6,7,8};
	cout << a.back() << endl;
	cout << a[2] << endl;
	//测试  blobptr 功能(string)
	blob<string> b = { "abc","def","ghi","jkl" };
	blobptr<string> ib2(b, 2);
	cout << *ib2 << endl;
	auto ib = b.begin();//合成版本拷贝
	cout<< *ib <<endl;
	cout<< *(++ib) <<endl;
	//检测const版本
	cout << "const版本功能测试" << endl;
	const blob<int> ca = { 1,2,3,4,5,6,7,8 };
	cout << ca.back() << endl;
	cout << ca[2] << endl;
	const blob<string> cb = { "abc","def","ghi","jkl" };
	auto icb = cb.begin();
	cout << *icb << endl;
}