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:

• Create a type definition

• Initialize LCM in your application

• Publish a message

• Subscribe to and receive a message

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

• Step 1: Creating a type definition

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

• Steps 2-4: C

• Steps 2-4: C++

• Steps 2-4: C# / .NET

• Steps 2-4: Java

• Steps 2-4: MATLAB

• Steps 2-4: Python

• Steps 2-4: Lua

• Steps 2-4: Go

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++.

Of course, serious projects will need a build system. LCM itself is built with CMake, and provides helper functions to simplify the binding generation process for projects built with CMake.

• Steps 5: Generating bindings with CMake

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
Go	listener/main.go	sender/main.go