当两个成员都在同一类中时，出现错误“非静态成员引用必须相对于特定对象”

Question

I know this question had been asked many times but I'm still stuck. I thought I got what this error was about what obviously I don't.

So, the error I am getting is

a nonstatic member reference must be relative to a specific object

My code is:

class theTranslator {
public:
    ros::NodeHandle nh;

    ros::Publisher pub = nh.advertise<sensor_msgs::Image>("camera/depth/image_raw", 100);

    static void getMessage(const sensor_msgs::Image::ConstPtr& recMmsg) {
        ROS_INFO( "I heard message" );
        pub.publish(recMmsg); //*** ERROR IS HERE ***
    }
};

since pub is part of the same class as getMessage() , shouldn't it work? How can I make a static member function use a variable member of the same class?

PS this is done in ROS (Robotics Operating System) but I believe this is a C++ mistake (not related to ROS).

Answer 1

In C++ you can not access a non static class member from a static method. Make it a normal method and try like below:-

 void getMessage(const sensor_msgs::Image::ConstPtr& recMmsg){
        ROS_INFO( "I heard message" );
        pub.publish(recMmsg); //*** ERROR IS HERE ***
    }

Else declare pub as static member

static ros::Publisher pub; 

Also refer to the below answer

C++ static member functions and variables

Answer 2

You need to make getMessage non-static or you need to make pub static.

Probably what you really need to do is rethink your design. Why are you trying to make getMessage static? As a very general rule of thumb static is a mistake, especially for a newbie.