LCM
Tutorial and examples

Introduction

LCM is a package designed to allow multiple processes to exchange messages in a safe and high-performance way. A message is the basic unit of LCM communications: it represents a self-contained piece of information. Messages are defined as programming language-independent data structures; the lcm-gen tool compiles these definitions into language-specific code.

Each message is sent on a channel, which is identified by a human-readable name. For example, messages containing information about the temperature in the hallway might be published on the "HALLWAY_TEMPERATURE" channel. By convention, all messages on a channel have the same type.

Any application can publish on any channel, although it is common for a single application serves as the sole source of data on a channel. Any application can receive data on any channel— for example, both a thermostat application and data logger might subscribe to the "HALLWAY_TEMPERATURE" channel.

This tutorial will walk you through the main tasks for exchange messages between two applications:

  1. Create a type definition
  2. Initialize LCM in your application
  3. Publish a message
  4. Subscribe to and receive a message

Since the type definitions are language independent, the first step is the same for all programming languages.

The remaining steps vary across programming languages, consult the following sections for language-specific tutorials.

Note that C and C++ are considered to be separate programming languages. It is possible to use the C bindings from C++, but there are also LCM bindings specific to C++.

Additional examples

Additional examples are provided with the source distribution of LCM.

For each language, at least two examples are provided. One listens for a message, the other transmits a message. The LCM type used is defined in example_t.lcm (examples/types/example_t.lcm in the source distribution).

Additional examples are distributed with the LCM source in the examples/ directory.

Language Listener Transmitter
C listener.c
listener-async.c
send_message.c
C++ listener.cpp send_message.cpp
C# example_t_display.cs example_t_transmit.cs
Java MySubscriber.java SendMessage.java
Lua listener.lua send-message.lua
MATLAB listener.m sendmessage.m
Python listener.py send-message.py