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Tutorial and examples {#tutorial_general}
====
# Introduction {#tutorial_general_intro}
LCM is a package designed to allow multiple processes to exchange messages in
a safe and high-performance way.
A <em>message</em> 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 <em>channel</em>, 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 \ref tut_lcmgen "first step" is the same
for all programming languages.
- \ref tut_lcmgen "Step 1: Creating a type definition"
The remaining steps vary across programming
languages, consult the following sections for language-specific tutorials.
- \ref tutorial_c "Steps 2-4: C"
- \ref tut_cpp "Steps 2-4: C++"
- \ref tut_dotnet "Steps 2-4: C# / .NET"
- \ref tut_java "Steps 2-4: Java"
- \ref tut_matlab "Steps 2-4: MATLAB"
- \ref tut_python "Steps 2-4: Python"
- \ref tut_lua "Steps 2-4: Lua"
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](https://github.com/lcm-proj/lcm/blob/master/examples/types/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](https://github.com/lcm-proj/lcm/blob/master/examples/c/listener.c) <br>[listener-async.c](https://github.com/lcm-proj/lcm/blob/master/examples/c/listener-async.c) | [send_message.c](https://github.com/lcm-proj/lcm/blob/master/examples/c/send_message.c)
C++ | [listener.cpp](https://github.com/lcm-proj/lcm/blob/master/examples/cpp/listener.cpp) | [send_message.cpp](https://github.com/lcm-proj/lcm/blob/master/examples/cpp/send_message.cpp)
C# | [example_t_display.cs](https://github.com/lcm-proj/lcm/blob/master/examples/csharp/example_t_demo/example_t_display.cs) | [example_t_transmit.cs](https://github.com/lcm-proj/lcm/blob/master/examples/csharp/example_t_demo/example_t_transmit.cs)
Java | [MySubscriber.java](https://github.com/lcm-proj/lcm/blob/master/examples/java/example_t_demo/MySubscriber.java) | [SendMessage.java](https://github.com/lcm-proj/lcm/blob/master/examples/java/example_t_demo/SendMessage.java)
Lua | [listener.lua](https://github.com/lcm-proj/lcm/blob/master/examples/lua/listener.lua) | [send-message.lua](https://github.com/lcm-proj/lcm/blob/master/examples/lua/send-message.lua)
MATLAB | [listener.m](https://github.com/lcm-proj/lcm/blob/master/examples/matlab/listener.m) | [sendmessage.m](https://github.com/lcm-proj/lcm/blob/master/examples/matlab/sendmessage.m)
Python | [listener.py](https://github.com/lcm-proj/lcm/blob/master/examples/python/listener.py) | [send-message.py](https://github.com/lcm-proj/lcm/blob/master/examples/python/send-message.py)
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