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I'm taking a sample I found on the web about how to get ROS and arduino to communicated together over serial. I have the sample working and now I'm moving the idea of the sample into my OOP project and am running into some trouble.

My sketch works but when I move a certain global variable to a protected member it breaks my sketch.

How do I declare this global variable

ros::Publisher chatter("chatter", &str_msg);

as a protected variable

protected:
  ros::Publisher chatter("chatter", &str_msg);

without getting this error

expected identifier before string constant

sample .ino

/*
 * rosserial Publisher Example
 * Prints "hello world!"
 */

#include <ros.h>
#include <std_msgs/String.h>

ros::NodeHandle nh;

std_msgs::String str_msg;
ros::Publisher chatter("chatter", &str_msg);

char hello[13] = "hello world!";

void setup()
{
  nh.initNode();
  nh.advertise(chatter);
}

void loop()
{
  str_msg.data = hello;
  chatter.publish( &str_msg );
  nh.spinOnce();
  delay(1000);
}

ROSController class

#include <ros.h>
#include <std_msgs/String.h>

class ROSController {
  protected:
    ros::NodeHandle _nh;
    std_msgs::String str_msg;
//    ros::Publisher chatter("chatter", &str_msg);
    int _throttle;
    bool _is_on = false;
  public:
    void loop();
    ROSController();
    double* getAttitude();
    bool isOn() {
      return this->_is_on;
    }
    int getThrottlePerc() {
      return this->_throttle / ROSController::THR_MAX;
    }

    static const int THR_MAX;
};

const int ROSController::THR_MAX = 100;

ROSController::ROSController() {
  this->_nh.initNode();
//  this->_nh.advertise(chatter);
}

double* ROSController::getAttitude() {
  return new double[3]{0, 0, 0};
}

void ROSController::loop() {
//  str_msg.data = new char[] {"hello"};
//  chatter.publish( str_msg );
  this->_nh.spinOnce();
  delay(1000);
}
  • I don't understand what you are trying to do there. Some context would be nice - ideally some actual code that demonstrates just what you are trying to do (before and after maybe?) – Majenko Sep 7 '16 at 23:07
  • I added my sample .ino and a little more of the backstory. It's really such a small issue so I was hoping I could keep the question just as simple but I suppose to be thorough you'll have to see the bigger picture. – Jacksonkr Sep 7 '16 at 23:12
  • And where are you trying to move that global variable to? – Majenko Sep 7 '16 at 23:13
  • I've added my ROSController class to the bottom of the question – Jacksonkr Sep 7 '16 at 23:16
  • 1
    There's no such thing as a "protected" global variable. Protected variables belong inside classes. – Nick Gammon Sep 7 '16 at 23:16
2

The problem you are having is you are trying to both define and declare a class member variable at the same time. You can't. Instead you need to split it:

protected:
    ros::Publisher chatter;

ROSController::ROSController() : chatter("chatter", &str_msg)
{
    this->_nh.initNode();
//  this->_nh.advertise(chatter);
}

That is, set up the variable as a protected member, then have the constructor call the constructor for you with the right parameters.

(I think that is the right syntax off the top of my head).

  • Then your Publisher class has no default constructor. Add one. – Majenko Sep 16 '16 at 10:27
  • Hey, that worked! I don't understand what you did on line 4. What is that called? I want to research it and find out more about it. – Jacksonkr Sep 16 '16 at 10:30
  • 1
    It's called an initialization list - you can read a little more about it here: tutorialspoint.com/cplusplus/cpp_constructor_destructor.htm – Majenko Sep 16 '16 at 10:31
0

You can't call the constructor in the class definition. Example:

class foo
  {
  protected:
    String bar ("fubar");
  };

void setup ()
  {
  }  // end of setup

void loop ()
  {
  }  // end of loop

That gives this error:

sketch_sep08b:4: error: expected identifier before string constant
     String bar ("fubar");
                 ^
sketch_sep08b:4: error: expected ',' or '...' before string constant
exit status 1
expected identifier before string constant

Instead declare the class (without the constructor) and call the constructor in the constructor for the parent class, like this:

class foo
  {
  protected:
    String bar;
  public:

    foo () : bar ("fubar") {};  // constructor
  };

void setup ()
  {
  }  // end of setup

void loop ()
  {
  }  // end of loop

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