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：[e-mail] */#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;   }