CODEWITHSUNDEEP
rossubscriberrospy
Bartek Czwartek
Bartek Czwartek

Reputation: 23

How to pass values from one subscriber's callback function to another in rosnode

My question is how to pass a value from one subscriber's callback function to another.

does this make sense ? 

import rospy
from sensor_msgs.msg import LaserScan, Int32
from xxx2.msg import xxyy2

global x
x = None      

def callback2(data):
    x=data[0]

def callback(data):
    if x > data.ranges[0]:
        print("nice")


rospy.Subscriber("/scan", LaserScan, callback)
rospy.Subscriber("topic", xxyy2, callback2)    
rospy.spin()

Upvotes: 2

Views: 4681

Answers (2)

Marco Arruda
Marco Arruda

Reputation: 709

I would change the code a bit, I think the way you have wrote it, the global variable is not properly setup.

The different is that instead of using the instruction global at the variable definition, you have to use it inside the callbacks.

import rospy
from sensor_msgs.msg import LaserScan, Int32
from xxx2.msg import xxyy2

x = None      

def callback2(data):
    global x
    x = data[0]

def callback(data):
    global x
    if x > data.ranges[0]:
        print("nice")


rospy.Subscriber("/scan", LaserScan, callback)
rospy.Subscriber("topic", xxyy2, callback2)    
rospy.spin()

Regards

Upvotes: 1

Malefitz
Malefitz

Reputation: 417

You can "pass" variable x to both callbacks as you can pass it to any other function, by making x global the way you did or by making x and the callback functions members of a class which allows you to just access them.

Callbacks are by default called sequentially so you don't need to worry about race conditions in this case.

Depending on your use case you can synchronize the callbacks with message filters if needed.

Upvotes: 1

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