Getting list of published topics from within C++ code

edit

You could

#include <ros/master.h>

and call

  ros::master::V_TopicInfo topic_infos;
  ros::master::getTopics(topic_infos);

This gets you topic infos (topic name and data type as std::strings) of all advertised topics; obviously not just those in vicon/ but you can filter them with boost:regex or e. g. split and check like:

  std::vector<std::string> lv_elems;

  char lc_delim[2];
  lc_delim[0] = '/';
  lc_delim[1] = '\0';

  boost::algorithm::split( lv_elems, topic_infos[0].name, boost::algorithm::is_any_of( lc_delim ) );

  if ( lv_elems[0] == "vicon" )
{
   // topic of topic_infos[0] is really in namespace vicon!!
}