C++11: smart pointer

#include <memory>#include <vector>#include <string>#include <iostream>#include <stdexcept>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();        std::string& front() const;        std::string& back() const;private:        std::shared_ptr<std::vector<std::string> > data;        void check(size_type i, const std::string &msg) const;};int main(){        StrBlob b1;         {                   StrBlob b2 = {"a", "an", "the"};                b1 = b2;                 b2.push_back("about");        }        while (b1.size() > 0) {                std::cout << b1.back() << " ";                b1.pop_back();        }        std::cout << "\n";        try {                std::cout << b1.back();        } catch (std::out_of_range &ex) {                std::cout << "file: " << __FILE__ << " line: " << __LINE__                          << " throw exception: " << ex.what() << std::endl;        }           std::cout << "aaaaaa\n";        return 0;}StrBlob::StrBlob(): data(std::make_shared<std::vector<std::string> >()) { }StrBlob::StrBlob(std::initializer_list<std::string> il)               : data(std::make_shared<std::vector<std::string> >(il)) { }void StrBlob::pop_back(){        check(0, "pop back on empty StrBlog");        data->pop_back();}std::string& StrBlob::front() const{        check(0, "front on empty StrBlob");        return data->front();}std::string& StrBlob::back() const{        check(0, "back on empty StrBlob");        return data->back();}void StrBlob::check(size_type i, const std::string &msg) const{        if (i >= data->size()) {                throw std::out_of_range(msg);        }}

// C++ primer 5th exercise 12.2(p.458)// g++ xx.cpp -std=c++11