How to use int or double as input to "arg" in ROS launch file

Question

I am trying to use the following as input values to an arg command in my roslaunch file as follows:

  <arg name="x_pos" value="3.0"/>
  <arg name="y_pos" value="4.0"/>
  <arg name="z_pos" value="0.0"/>
  <arg name="yaw" value="0.0"/>

However, the doubles I entered do not show up when I try to access them from my C++ node; I read the arg attributes and they do not mention anything about the type of value. Is it by default only string? If that's the case, how do I pass in the doubles so that I can access them in my C++ node?

Answer 1

As there is no C++ code mentioned in the question, I wonder if I understood your requirements correctly. However, I never faced issues with integers or double datatypes with the ROS launch file. Below is a code snippet:

ROS launch file:

  <!-- your integer arguments -->
  <arg name="k_neighbors" default="10"/>
  <arg name="max_itr" default="1000"/>

  <!-- your double arguments -->
  <arg name="weight" default="0.05"/>
  <arg name="d_thresh" default="0.005"/>
  <arg name="prob" default="0.99999"/>

  <!-- your float arguments -->
  <arg name="radius" default="0.05"/>

  <!-- your string arguments -->
  <arg name="limb" default="right"/>

C++ node:

int main(int argc, char **argv)
{
  ros::init(argc, argv, "my_node");
  ros::NodeHandle nh("~");

  // define integer parameter and then fetch their values from parameter server
  int k_neighbors, max_itr;
  nh.getParam("k_neighbors", k_neighbors);
  nh.getParam("max_itr", max_itr);

  // define double parameter and then fetch their values from parameter server
  double weight, d_thresh, prob;
  nh.getParam("weight", weight);
  nh.getParam("d_thresh", d_thresh);
  nh.getParam("prob", prob);

  // define float parameter and then fetch their values from parameter server
  float sphere_radius;
  nh.getParam("radius", sphere_radius);

  // define string parameter and then fetch their values from parameter server
  std::string limb;
  nh.getParam("limb", limb);

  // rest of your logic goes here
  return 0;
}

You may look for launch file and C++ node.

Answer 2

I looked at github issue "Can't pass in a numerical string as arg param to C++ node" and found that putting single quotes around the double, within double quotes, works:

  <arg name="x_pos" value="'3.0'"/>
  <arg name="y_pos" value="'4.0'"/>
  <arg name="z_pos" value="'0.0'"/>
  <arg name="yaw" value="'0.0'"/>