如何为 cv::Filestorage 重载 << 运算符？

Question

我想使用 cv::FileStorage 类将我的 MarkerDistance 结构写入文件。

我尝试以各种方式重载

struct MarkerDistance
{
    std::string linkName;
    double distance;

    MarkerDistance(std::string a, double b)
    {
        linkName = a;
        distance = b;
    }
    //Version 1
    cv::FileStorage & MarkerDistance::operator<< (cv::FileStorage &  fs)
    {
        std::string link = "linkName : " + linkName + "\n";
        std::string dist = "distance : " + std::to_string(distance) + "\n";
        std::string erg = link + dist;
        fs << erg;
    }

    //Version 2
    std::ostream& MarkerDistance::operator << (std::ostream& os)
    {
       // write obj to stream
       std::string link = "linkName : " + linkName + "\n";
       std::string dist = "distance : " + std::to_string(distance) + "\n";
       std::string erg = link + dist;
       return os << erg;
    }
};

错误信息：

Answer 1

您的operator<< 应具有以下签名：

std::ostream& MarkerDistance::operator<<(std::ostream& os, const MarkerDistance& obj);

或

cv::FileStorage& MarkerDistance::operator<<(cv::FileStorage& os, const MarkerDistance& obj);