ros::spin();

`ros::spin()` 是ROS的一个函数，它是一个循环函数，用于处理ROS的回调函数和消息队列。在ROS节点中，当节点启动后，它需要一直运行以便能够接收和处理来自其他节点的消息。而 `ros::spin()` 就是用来让节点保持运行的函数。当 `ros::spin()` 被调用时，它会一直运行直到节点被关闭或者被 `ros::shutdown()` 停止。在循环中，它会不断检查是否有新的消息需要处理，并调用相应的回调函数来处理这些消息。

相关问题

ros::spinOnce() ros::spin()

In ROS, there are two commonly used functions for handling callbacks: ros::spinOnce() and ros::spin().

ros::spinOnce() allows ROS to process any pending callbacks once, but then returns control to the calling thread. This is useful when you have a loop that needs to keep running, but you need to periodically check for new data or events.

ros::spin(), on the other hand, is a blocking call that does not return control to the calling thread until the node is shut down. This is useful when you have a node that needs to run continuously and respond to events or data as they come in.

In general, you should use ros::spinOnce() if you have a loop that needs to keep running, and ros::spin() if you have a node that needs to run continuously. However, there are some cases where you may need to use both functions together, such as if you have multiple nodes running in the same process.

ros::Timer timer = nh.createTimer(ros::Duration(0), creat_callback); ros::spin()

这段代码创建了一个周期为0秒的ROS计时器，并指定当计时器超时时调用名为`creat_callback`的回调函数。接着，通过调用`ros::spin()`函数来使ROS节点进入自循环状态，等待来自ROS系统的事件（例如计时器超时事件、消息到达事件等）。在自循环状态下，ROS会不断地检查是否有事件发生，如果有则会调用相应的回调函数来处理事件。因为计时器的周期为0秒，所以它会立即超时并执行回调函数。而通过调用`ros::spin()`函数，ROS节点会一直等待事件的发生，直到节点被关闭。所以这段代码会在计时器超时后执行回调函数，并一直等待事件的发生，直到节点被关闭。