[c++] rosparam server : How to transform a set of parameters of type XmlRpc::XmlRpcValue into some multi-type dictionnary or array ?

asked 2018-12-04 12:10:52 -0500

ftre gravatar image

updated 2018-12-07 04:47:39 -0500


When doing rosparam list in a shell while an instance of ros is running, I get a list of "keys" or paths, e.g :


Now as explained here http://wiki.ros.org/Parameter%20Server it seems to be possible to fetch a dictionnary if we rosparam get /ros/family which would be displayed into console as if it was written respecting the .yaml indentations. In this case the console output would be :

a : {a_first_param : somevalue},
b : {b_first_param : somevalue, b_second_param : somevalue, b_third_param : somevalue},
c : {c_first_param : somevalue, c_second_param : somevalue}

I suspect this output to be of type XmlRpc::XmlRpcValue. Besides, this output would have that .yaml file as an equivalent :

        a_first_param: somevalue #int
        b_first_param: somevalue #double
        b_second_param: somevalue #string
        b_third_param: somevalue #boolean
        c_first_param: somevalue #list
        c_second_param: somevalue

Finally, let's say I am actually only interested in the parameters associated to b, but I cannot prevent the whole family to be loaded on the parameter server. Then I would like to create a function which reads this bunch of parameters and returns only those associated to b. Furthermore, these parameters' names aren't known in advance, and neither the number of these, and neither their value.

I would ideally like the output to be a multi-type dictionary, which, as far as I know, doesn't exist in c++. So a struct or an [n rows, 2 columns] array would suit me, as long as I am then able to find back the name of the attributes and their value in order to tweak those same parameters. (Preferably by replacing the whole set, but it will still be feasible individually, so less worries for that.)

So my c++ snippet looks like that :

<namespace::WhichType?> getParameters();
XmlRpc::XmlRpcValue parameters;
if (ros::param::get("ros/family", parameters))
  return parameters.structFromXml(); // or .arrayFromXml()

Unfortunately, this dochttp://xmlrpcpp.sourceforge.net/doc/c... indicates that prototype for .structFromXml():

bool    structFromXml (std::string const &valueXml, int *offset)

So what is valueXml ? Is it the path "ros/family" ? Is it the outputed variable that will contains either my struct or array ? What should I put as 2nd argument (about the offset) please ?


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