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

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{{Getting Started with ROS on Embedded Systems/Head|previous=User Guide/C++/Topics|next=User Guide/C++/Publishers_and_subscribers|keywords=ROS}}
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{{Getting Started with ROS on Embedded Systems/Head|previous=User Guide/C++/Messages|next=User Guide/C++/Publishers_and_subscribers|metakeywords=ROS}}
  
 
== 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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A useful function is a 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 pre-appended to your topic names.
  
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* M is the message type to publish on the topic
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Another function is the append, which simply appends two strings resulting in left/right
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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:
 
  
 
<syntaxhighlight lang="cpp">
 
<syntaxhighlight lang="cpp">
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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());
 
 
</syntaxhighlight>
 
</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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{{Getting Started with ROS on Embedded Systems/Foot|User Guide/C++/Messages|User Guide/C++/Publishers_and_subscribers}}
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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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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);
 
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</syntaxhighlight>
 

Latest revision as of 13:15, 8 March 2023




Previous: User Guide/C++/Messages Index Next: User Guide/C++/Publishers_and_subscribers


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



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

A useful function is a 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 pre-appended 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);


Previous: User Guide/C++/Messages Index Next: User Guide/C++/Publishers_and_subscribers


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