nros C API

Lightweight ROS 2 client library for embedded real-time systems.

Quick Start

#include <rclc/rclc.h>
#include <std_msgs/msg/int32.h> /* generated by nano_ros_generate_interfaces() */
 
/* Initialise the support context (transport layer). The allocator is rcl's
 * argument; nothing here allocates. */
rcl_allocator_t allocator = rcl_get_default_allocator();
rclc_support_t support = rclc_support_get_zero_initialized();
rclc_support_init(&support, 0, NULL, &allocator);
 
/* Create a node. */
rcl_node_t node = rcl_get_zero_initialized_node();
rclc_node_init_default(&node, "my_node", "", &support);
 
/* Create a publisher and publish. */
rcl_publisher_t pub = rcl_get_zero_initialized_publisher();
rclc_publisher_init_default(&pub, &node, ROSIDL_GET_MSG_TYPE_SUPPORT(std_msgs, msg, Int32),
                            "chatter");
std_msgs__msg__Int32 msg = {.data = 42};
rcl_publish(&pub, &msg, NULL);
 
/* Tear down in reverse order. */
rcl_publisher_fini(&pub, &node);
rcl_node_fini(&node);
rclc_support_fini(&support);

API Modules

The API is organised into the following module groups (see the Modules tab in the sidebar for each group's contents):

Group	Description
init	Library initialisation, support context
node	Node creation and lifecycle
pubsub	Topic publishers and subscriptions
service	Service servers and clients
action	Action servers and clients
executor	Callback executor, timers, guard conditions
clock	Clock and time types
parameter	Parameter services
lifecycle	Node lifecycle state machine (REP-2002)
cdr	CDR serialisation helpers
qos	Quality-of-Service settings
errors	Return codes, see Error Codes
types	Shared types

Header Organisation

Each per-module header above is the authoritative C API surface for its module, with hand-written Doxygen documentation. Include individual headers for what you need, or use <rclc/rclc.h> for everything.

Shared types (return codes, QoS, time) live in <rclc/types.h>, which all module headers include automatically.

An internal nros_generated.h (produced by cbindgen) is used for compile-time drift detection — it is not part of the public API.

Reference

• Error Codes — rcl_ret_t reference with cause and recovery

Guides

• Getting Started — project setup, CMake integration, and code generation
• Configuration — environment variables and buffer tuning
• ROS 2 Interoperability — interoperability with ROS 2 via rmw_zenoh
• Troubleshooting — common issues and solutions