未写入矢量的值

我正在尝试从对象的构造函数中的文件中读取对值。

该文件如下所示：

4
1 1
2 2
3 3
4 4

第一个数字是要读取的对数。

在某些行中，值似乎已正确写入向量。接下来他们就走了。我完全困惑了

inline
BaseInterpolator::BaseInterpolator(std::string data_file_name)
{
    std::ifstream in_file(data_file_name);
    if (!in_file) {
        std::cerr << "Can't open input file " << data_file_name << std::endl;
        exit(EXIT_FAILURE);
    }
    size_t n;
    in_file >> n;
    xs_.reserve(n);
    ys_.reserve(n);
    size_t i = 0;
    while(in_file >> xs_[i] >> ys_[i])
    {
        // this line prints correct values i.e. 1 1, 2 2, 3 3, 4 4
        std::cout << xs_[i] << " " << ys_[i] << std::endl;
        // this lines prints xs_.size() = 0
        std::cout <<  "xs_.size() = " << xs_.size() << std::endl;
        if(i + 1 < n)
            i += 1;
        else
            break;
        // this line prints 0 0, 0 0, 0 0
        std::cout << xs_[i] << " " << ys_[i] << std::endl;
    }
    // this line prints correct values i.e. 4 4    
    std::cout << xs_[i] << " " << ys_[i] << std::endl;
    // this lines prints xs_.size() = 0
    std::cout <<  "xs_.size() = " << xs_.size() << std::endl;
}

该类定义如下：

class BaseInterpolator
{
public:
    ~BaseInterpolator();
    BaseInterpolator();
    BaseInterpolator(std::vector<double> &xs, std::vector<double> &ys);
    BaseInterpolator(std::string data_file_name);
    virtual int interpolate(std::vector<double> &x, std::vector<double> &fx) = 0;
    virtual int interpolate(std::string input_file_name,
                        std::string output_file_name) = 0;

protected:
    std::vector<double> xs_;
    std::vector<double> ys_;
};