c++ - 如何解决访问不同函数的 "nonstatic member reference must be relative to a specific object"

Question

我正在尝试将一些用于测试的函数传递到 main() 节点中，如下所示。但是，我得到以下信息 non static member reference must be relative to a specific object。我正在对这个问题进行大量研究，例如我发现 this也有类似的问题this is useful那是在解释如何访问和理解与“父”实例的关系。我应用了建议 here多亏了传递 madgwick::MADGWICK_reader obj(std::string file); 在主体上，我能够部分访问具有函数 的 class MADGWICK_reader >void filter_function(const sensor_msgs::Imu &msg); 我正在尝试从 main 访问，但仍然有些地方不完全正确。

我知道通过简单地添加“static”关键字来使成员静态化是不正确的，我也需要定义它们，这就是为什么函数专门设置为void的原因filter_function(const sensor_msgs::Imu &msg);我传递 ampersend & 是为了通过对 main 的引用传递它，但似乎从未收到该函数。

这是 ma​​dgwick_filter.h，注意 void filter_function(const sensor_msgs::Imu &msg); 函数在 main< 中有问题:

namespace madgwick
{
    using timestamp_t = uint64_t;
    using timestampToDouble_t = double;

    struct IMU_MADGWICK_DATA
    {
        double magz;
        double magy;
        double magx;
        float accelz;
        float accelx;
        float accely;
        unsigned long timestamp;
        double phi;   // orientation
        double psi;   // orientation
        double theta; // orientation
        double gyrox; // angular velocity x
        double gyroy; // angular velocity y
        double gyroz; // angular velocity z
    };


    class Madgwick
    {
    public:
      Madgwick();

    };

    class MADGWICK_reader
    {
    public:
        MADGWICK_reader(std::string filename);
        bool nextLine();
        bool nextLineWithSupport();

        IMU_MADGWICK_DATA madgwick_data;

        sensor_msgs::Imu imuMadgwickMsg;
        sensor_msgs::MagneticField magMedgwickMsg;

        geometry_msgs::QuaternionStamped q;
        geometry_msgs::Vector3Stamped v;
        geometry_msgs::TransformStamped q_trans;
        float sampleFreq;
        double beta;
        double q0=1.0, q1=0.0, q2=0.0, q3=0.0;
        std_msgs::Header header;
        float ax, ay, az, gx, gy, gz;
        ros::Duration dtime;
        float dt;

        float invSqrt();
        void qua2Euler(geometry_msgs::QuaternionStamped);
        void madgwickIMU(float gx, float gy, float gz, float ax, float ay, float az);
        void filter_function(const sensor_msgs::Imu &msg);

    private:
        io::CSVReader<13> madg_imu_reader;
        unsigned int imuMadgNum;
        unsigned int magMadgNum;
        void packMadgMagMsg();
        void pack_Imu_Madgwick_Msg();
        void pack_Mag_Madgwick_Msg();
    };
}

ma​​dgwick_filter.cpp

namespace madgwick
{
    Madgwick::Madgwick()
    {

    }

    MADGWICK_reader::MADGWICK_reader(std::string filename):
        madg_imu_reader(filename)
    {
        // operations ...
    }

    void MADGWICK_reader::filter_function(const sensor_msgs::Imu &msg)
    {
        timestampToDouble_t currentTime = (madgwick_data.timestamp)/1e6;
        ros::Time stamp(currentTime);
        header = msg.header;
        ax = float(msg.linear_acceleration.x);
        ay = float(msg.linear_acceleration.y);
        az = float(msg.linear_acceleration.z);

        // more operations ...
    }
}

最后是 ma​​dgwick_filter_node.cpp

#include "imu_filter_madgwick/madgwick_filter.h"
#include <iostream>

    int main(int argc, char** argv)
    {
        ros::init(argc, argv, "madgwick_filter_node");
        madgwick::MADGWICK_reader reader(std::string filename);

        ros::NodeHandle n;
        ros::Publisher pub1 = n.advertise<geometry_msgs::QuaternionStamped>("quaternion", 1);
        ros::Publisher pub2 = n.advertise<geometry_msgs::Vector3Stamped>("ypr", 1);

        tf::TransformBroadcaster q_brodecaster;

        madgwick::MADGWICK_reader obj(std::string file);

        ros::Subscriber sub = n.subscribe("imu0", 10, obj.filter_function); // <-- Error Here

        ros::spin();
    }

谁能指出正确的方向或解释为什么仍然无法从 main 访问类中包含的函数？感谢您阐明这一点。

Answer 1

由于您没有提供订阅声明，但您的问题似乎与将类成员函数传递给其他函数有关，因此下面的解决方案提供了两种实现方法，一种通过 lambda，另一种通过绑定(bind)。

#include <iostream>
#include <functional>
class Test{
    public:
    void fun(int x)
    {
        std::cout<<"I am having fun in Test with number "<<x<<std::endl;
    }
};
void sampleFunction(std::function<void(int)> sf,int x)
{
    sf(x);
}
int main()
{
    Test obj;
    auto objf = std::bind(&Test::fun,&obj,std::placeholders::_1);
    sampleFunction(objf,5);

    auto lf = [&obj](int y) { return obj.fun(y); };
    sampleFunction(lf,6);
    return 0;
}