Difference between revisions of "Getting Started with ROS on Embedded Systems/User Guide/C++/Names"

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== Introduction ==
 
== Introduction ==
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This wiki is based on the following page: http://wiki.ros.org/roscpp/Overview/Publishers%20and%20Subscribers
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This wiki is based on the following page: http://wiki.ros.org/roscpp/Overview/Names%20and%20Node%20Information
  
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Publishers and subscribers are one of the main ways of communication when using ROS.
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Name manipulation is an important section for ROS, in here you can find useful functions that work well when doing this manipulation
  
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== Publishers ==
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== Functions ==
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In order to publish messages, you will need a node handle, and create a ros::Publisher using the advertise function. Like the following example:
 
  
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<syntaxhighlight lang="cpp">
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An useful function is the resolve, which lets you create a name with the namespace of the node and a given name, resulting in node_namespace/name
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ros::Publisher pub = nh.advertise<std_msgs::String>("topic_name", 5);
 
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std_msgs::String str;
 
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str.data = "hello world";
 
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pub.publish(str);
 
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</syntaxhighlight>
 
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This uses the function
 
  
 
<syntaxhighlight lang="cpp">
 
<syntaxhighlight lang="cpp">
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template<class M>
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std::string ros::names::resolve(const std::string& name, bool remap = true);
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ros::Publisher advertise(const std::string& topic, uint32_t queue_size, bool latch = false);
 
 
</syntaxhighlight>
 
</syntaxhighlight>
  
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In which:
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This is useful when you don't want to have the node name preappended to your topic names.  
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* M is the message type to publish on the topic
 
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* topic is the name of the topic to publish to
 
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* queue_size is the size of the message queue, if the publishing is faster than the message sending, it will start dropping older messages.
 
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* latch: Save messages for future subscriber connections automatically.
 
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== Subscribers ==
 
  
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Similar to publishers, a ROS subscriber needs a node handle and with the subscribe function it will create a new ros::Subscriber, by using the following:
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Another function is the append, which simply appends two strings resulting in left/right
  
 
<syntaxhighlight lang="cpp">
 
<syntaxhighlight lang="cpp">
−
template<class M>
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std::string ros::names::append(const std::string& left, const std::string& right);
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ros::Subscriber subscribe(const std::string& topic, uint32_t queue_size, <callback, which may involve multiple arguments>, const ros::TransportHints& transport_hints = ros::TransportHints());
 
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</syntaxhighlight>
 
−
 
 
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In which:
 
−
 
 
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* M is the message type to publish on the topic, normally deduced by the compiler
 
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* topic is the name of the topic to subscribe to
 
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* queue_size is the size of the message queue, if messages are too fast arriving and the application can't keep up, they will start dropping.
 
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* callback: Normally a pointer to a function with the function to execute on each message arrival
 
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* transport_hints: Hints to roscpp's transport layer. Such ad preferring UDP, tcp nodelay.
 
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===Callbacks===
 
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The first callback you can use is with a function, for example:
 
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<syntaxhighlight lang="cpp">
 
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void callback(const std_msgs::StringConstPtr& str)
 
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{
 
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...
 
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}
 
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...
 
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ros::Subscriber sub = nh.subscribe("my_topic", 1, callback);
 
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</syntaxhighlight>
 
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−
 
 
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The other callback is used with class methods, for example:
 
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<syntaxhighlight lang="cpp">
 
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void Foo::callback(const std_msgs::StringConstPtr& message)
 
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{
 
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}
 
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...
 
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Foo foo_object;
 
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ros::Subscriber sub = nh.subscribe("my_topic", 1, &Foo::callback, &foo_object);
 
 
</syntaxhighlight>
 
</syntaxhighlight>

Revision as of 12:42, 10 November 2021




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Getting Started with ROS
on Embedded Systems
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ROS on Embedded Systems Basics
Getting Started
C++ User Guide
Examples
Performance
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Introduction

This wiki is based on the following page: http://wiki.ros.org/roscpp/Overview/Names%20and%20Node%20Information

Name manipulation is an important section for ROS, in here you can find useful functions that work well when doing this manipulation

Functions

An useful function is the resolve, which lets you create a name with the namespace of the node and a given name, resulting in node_namespace/name 

std::string ros::names::resolve(const std::string& name, bool remap = true);

This is useful when you don't want to have the node name preappended to your topic names.

Another function is the append, which simply appends two strings resulting in left/right 

std::string ros::names::append(const std::string& left, const std::string& right);
Retrieved from "http://developer.ridgerun.com/wiki/index.php?title=Getting_Started_with_ROS_on_Embedded_Systems/User_Guide/C%2B%2B/Names&oldid=37190"