Use empty() to check for an empty string (#247)

* rmw_fastrtps_shared_cpp/src/demangle.cpp:
    * rmw_fastrtps_shared_cpp/src/rmw_node_info_and_types.cpp:
    * rmw_fastrtps_shared_cpp/src/rmw_service_names_and_types.cpp:

Author: jwillemsen

rmw_fastrtps_shared_cpp/src/demangle.cpp

@@ -52,7 +52,7 @@ std::string
 _demangle_service_from_topic(const std::string & topic_name)
 {
   std::string prefix = _get_ros_prefix_if_exists(topic_name);
-  if (!prefix.length()) {
+  if (prefix.empty()) {
     // not a ROS topic or service
     return "";
   }

rmw_fastrtps_shared_cpp/src/rmw_node_info_and_types.cpp

@@ -416,13 +416,13 @@ __rmw_get_service_names_and_types_by_node(
     if (node_topics != topic_cache.getParticipantToTopics().end()) {
       for (auto & topic_pair : node_topics->second) {
         std::string service_name = _demangle_service_from_topic(topic_pair.first);
-        if (!service_name.length()) {
+        if (service_name.empty()) {
           // not a service
           continue;
         }
         for (auto & itt : topic_pair.second) {
           std::string service_type = _demangle_service_type_only(itt);
-          if (service_type.length()) {
+          if (!service_type.empty()) {
             services[service_name].insert(service_type);
           }
         }

rmw_fastrtps_shared_cpp/src/rmw_service_names_and_types.cpp

@@ -72,13 +72,13 @@ __rmw_get_service_names_and_types(
       std::lock_guard<std::mutex> guard(topic_cache.getMutex());
       for (auto it : topic_cache.getTopicToTypes()) {
         std::string service_name = _demangle_service_from_topic(it.first);
-        if (!service_name.length()) {
+        if (service_name.empty()) {
           // not a service
           continue;
         }
         for (auto & itt : it.second) {
           std::string service_type = _demangle_service_type_only(itt);
-          if (service_type.length()) {
+          if (!service_type.empty()) {
             services[service_name].insert(service_type);
           }
         }