C++Primer第五版 练习12.2

练习12.2：编写你自己的StrBlob类，包含const版本的front和back。

/*
*2015/10/28
*练习12.2 
*问题描述：练习12.2：编写你自己的StrBlob类，包含const版本的front和back
*作者：Nick Feng 
*邮箱：nickgreen23@163.com 
*/

#include <iostream>
#include <string>
#include <vector>
#include <memory>

using namespace std;

class StrBlob{
public:
    typedef std::vector<std::string>::size_type size_type;
    StrBlob();
    StrBlob(std::initializer_list<std::string> il);
    size_type size() const { return data->size();}
    bool empty() const { return data->empty();}
    void push_back(const std::string &t) { data->push_back(t);}
    void pop_back();
    const std::string& front();
    const std::string& back();
private:
    std::shared_ptr<std::vector<std::string>> data;
    void check(size_type i, const std::string &msg) const;
};

StrBlob::StrBlob() : data(make_shared<vector<string>>()) { }

StrBlob::StrBlob(initializer_list<string> il) : data(make_shared<vector<string>>(il)){ }

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

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

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

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

int main()
{
    StrBlob b1;
    StrBlob b2 = {"a","an","the"};
    b1 = b2;
    b2.push_back("about");


    cout << b1.size() << endl;
    cout << b2.size() << endl;
    return 0;   
}