c++ primer中的一个练习push_back时读取访问权限冲突

[iimmw]

#ifndef STRBLOB
#define STRBLOB
#include <iostream>
#include <memory>
#include <vector>
#include <string>
#include <fstream>
using std::vector;
using std::string;

class StrBlobPtr;
class StrBlob {
	friend class StrBlobPtr;
public:
	typedef vector<string>::size_type size_type;
	StrBlob();
	StrBlob(std::initializer_list<string> il);
	size_type size()const { return data->size(); };
	bool empty()const { return data->empty(); };
	//添加和删除元素
	void push_back(const string &t) { data->push_back(t); };
	void pop_back();
	//元素访问
	string& front();
	string& front() const;
	string& back();
	string& back() const;
	//返回指向首元素和尾后元素的StrBlobPtr
	StrBlobPtr begin();
	StrBlobPtr end();
private:
	std::shared_ptr<vector<string>> data;
	void check(size_type i, const string& msg) const;
};


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

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

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

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

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



class StrBlobPtr {
public:
	StrBlobPtr() :curr(0) {}
	StrBlobPtr(StrBlob &a, size_t sz = 0) :
		wptr(a.data), curr(sz) {}
	std::string& deref()const;
	StrBlobPtr& incr();	//前缀递增
private:
	//若检查成功，check返回一个指向vector的shared_ptr
	std::shared_ptr<vector<string>>
		check(std::size_t, const std::string&)const;
	//保存一个weak_ptr，意味着底层vector可能会被销毁
	std::weak_ptr <vector<string>>wptr;
	std::size_t curr;	//在数组中的位置
};

std::shared_ptr<vector<string>>
StrBlobPtr::check(std::size_t i, const string &msg)const
{
	auto ret = wptr.lock();		//wptr所指的vector还存在吗
	if (!ret)
		throw std::runtime_error("unbound StrBlobPtr");
	if (i >= ret->size())
		throw std::out_of_range(msg);
	return ret;	//否则返还指向vector的shared_ptr
}

std::string& StrBlobPtr::deref()const
{
	auto p = check(curr, "dereference past end");
	return (*p)[curr];	//返回vector的curr坐标的字符串
}

StrBlobPtr& StrBlobPtr::incr()
{
	//如果curr已经指向容器的尾后位置，就不能递增它
	check(curr, "increment past end of StrBlobPtr");
	++curr;	//推进当前位置
	return *this;
}

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

#endif

int main()
{
	std::ifstream in("str.txt");
	if (!in) {
		std::cout << "open error!" << std::endl;
		return -1;
	}

	StrBlob blob;
	for (std::string str; std::getline(in, str);) blob.push_back(str);

	return 0;
}

在main函数里一调用blob类的push_back就会异常并中断，新手想了好久还是不知道问题在哪里，求大神解答....

[sdghchj]

成员data没有指向vector对象。 修改构造函数： StrBlob::StrBlob() { data = std::make_shared<std::vector>(); };

[iimmw]

引用 1 楼 sdghchj 的回复:

成员data没有指向vector对象。 修改构造函数： StrBlob::StrBlob() { data = std::make_shared<std::vector>(); };

噢噢噢噢我明白了谢谢你！