Zero init topic names and types (#85)

* initialize topic_names_and_type struct in rcl

* sanity check in get_topic_names_and_types

* uncrustify

* initialize all fields...

* address documentation request

* typo

rcl/include/rcl/graph.h

@@ -32,13 +32,19 @@ extern "C"
 
 typedef rmw_topic_names_and_types_t rcl_topic_names_and_types_t;
 
+
+/// Return a rcl_topic_names_and_types_t struct with members initialized to NULL.
+RCL_PUBLIC
+RCL_WARN_UNUSED
+rcl_topic_names_and_types_t
+rcl_get_zero_initialized_topic_names_and_types(void);
+
 /// Return a list of topic names and their types.
 /* This function returns a list of topic names in the ROS graph and their types.
  *
  * The node parameter must not be NULL, and must point to a valid node.
  *
- * The topic_names_and_types parameter must not be NULL, and must point to an
- * already allocated rcl_topic_names_and_types_t struct.
+ * The topic_names_and_types parameter must be allocated and zero initialized.
  * The topic_names_and_types is the output for this function, and contains
  * allocated memory.
  * Therefore, it should be passed to rcl_destroy_topic_names_and_types() when

rcl/include/rcl/node.h

@@ -80,7 +80,7 @@ rcl_get_zero_initialized_node(void);
  * This function will create those external parameter interfaces even if
  * parameters are not used later.
  *
- * The rcl_node_t given must be allocated and zero initalized.
+ * The rcl_node_t given must be allocated and zero initialized.
  * Passing an rcl_node_t which has already had this function called on it, more
  * recently than rcl_node_fini, will fail.
  * An allocated rcl_node_t with uninitialized memory is undefined behavior.

rcl/src/rcl/graph.c

@@ -21,6 +21,13 @@ extern "C"
 
 #include "./common.h"
 
+rcl_topic_names_and_types_t
+rcl_get_zero_initialized_topic_names_and_types(void)
+{
+  const rcl_topic_names_and_types_t null_topic_names_and_types = {0, NULL, NULL};
+  return null_topic_names_and_types;
+}
+
 rcl_ret_t
 rcl_get_topic_names_and_types(
   const rcl_node_t * node,
@@ -31,6 +38,18 @@ rcl_get_topic_names_and_types(
     return RCL_RET_NODE_INVALID;
   }
   RCL_CHECK_ARGUMENT_FOR_NULL(topic_names_and_types, RCL_RET_INVALID_ARGUMENT);
+  if (topic_names_and_types->topic_count != 0) {
+    RCL_SET_ERROR_MSG("topic count is not zero");
+    return RCL_RET_INVALID_ARGUMENT;
+  }
+  if (topic_names_and_types->topic_names) {
+    RCL_SET_ERROR_MSG("topic names is not null");
+    return RCL_RET_INVALID_ARGUMENT;
+  }
+  if (topic_names_and_types->type_names) {
+    RCL_SET_ERROR_MSG("type names is not null");
+    return RCL_RET_INVALID_ARGUMENT;
+  }
   return rmw_get_topic_names_and_types(
     rcl_node_get_rmw_handle(node),
     topic_names_and_types