C++ Primer（第5版） 练习 12.20

练习 12.20 编写程序，逐行读入一个输入文件，将内容存入一个StrBlob中，用一个StrBlobPtr打印出StrBlob中的每个元素。

环境：Linux Ubuntu（云服务器）

工具：vim

代码块

/*************************************************************************
	> File Name: ex12.20.cpp
	> Author: 
	> Mail: 
	> Created Time: Thu 18 Apr 2024 09:15:15 AM CST
 ************************************************************************/

#include<iostream>
#include<fstream>
#include<sstream>
#include<string>
#include<vector>
#include<memory>
using namespace std;

class StrBlobPtr;

class StrBlob{
    friend class StrBlobPtr;

    public:
	typedef vector<string>::size_type size_type;
    StrBlob(): data(make_shared<vector<string>>()) {}
    StrBlob(initializer_list<string> il): data(make_shared<vector<string>>(il)) {}
	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();
	string &front();
	string &back();
	string &front() const;
	string &back() const;

    StrBlobPtr begin();
    StrBlobPtr end();

    private:
	shared_ptr<vector<string>> data;
	void check(size_type i, const string &msg) const;
};

void StrBlob::pop_back(){
	check(0, "pop_back on empty StrBlob");
	data->pop_back();
}

string& StrBlob::front(){
	check(0, "front on empty StrBlob");
	return data->front();
}

string& StrBlob::back(){
	check(0, "back on empty StrBlob");
	return data->back();
}

string& StrBlob::front() const{
	check(0, "front on empty StrBlob");
	return data->front();
}

string& StrBlob::back() const{
	check(0, "back on empty StrBlob");
	return data->back();
}

void StrBlob::check(size_type i, const string &msg) const{
	if(i >= data->size()){
		throw out_of_range(msg);
	}
}

class StrBlobPtr{
    friend bool compare(StrBlobPtr &a, const StrBlobPtr &b);

    public:
    StrBlobPtr(): curr(0) {}
    StrBlobPtr(StrBlob &s, size_t sz = 0): wptr(s.data), curr(sz) {}
    string &deref() const;
    StrBlobPtr &incr();

    private:
    shared_ptr<vector<string>> check(size_t, const string &) const;
    weak_ptr<vector<string>> wptr;
    size_t curr;
};

shared_ptr<vector<string>> StrBlobPtr::check(size_t i, const string &msg) const {
    auto ret = wptr.lock();
    if(!ret){
        throw runtime_error("unbound StrBlobPtr");
    }
    if(i >= ret->size()){
        throw out_of_range(msg);
    }
    return ret;
}

string &StrBlobPtr::deref() const{
    auto p = check(curr, "dereference past end");
    return (*p)[curr];
}

StrBlobPtr &StrBlobPtr::incr(){
    check(curr, "increment past end of StrBlobPtr");
    ++curr;
    return *this;
}

StrBlobPtr StrBlob::begin(){
    return StrBlobPtr(*this);
}

StrBlobPtr StrBlob::end(){
    return StrBlobPtr(*this, data->size());
}

bool compare(StrBlobPtr &a, const StrBlobPtr &b){
    if(a.wptr.lock() == b.wptr.lock() && a.curr == b.curr){
        return true;
    }
    return false;
}

int main(){
    ifstream in("12.20.txt");
    StrBlob file;
    string str;
    StrBlobPtr nFile(file);

    while(getline(in, str)){
        file.push_back(str);
    }

    for(auto it = file.begin(); !compare(it, file.end()); it.incr()){
        cout<<it.deref()<<" ";
    }
    cout<<endl;

    in.close();

    return 0;
}

运行结果显示如下