Is it possible to use a certain data value of a topic for executing some code?

edit

Thank you for your reply! Since i don't know how to check the topic values, can you please try to explain it to me? Below there is the code:

void orderCallback()
{
chdir("/home/marco/catkin_ws/src/heart_rate_monitor");

system("get_hrv -R my_data_file.txt >doc.txt");
}

@mig This is the subscriber:

ros::Subscriber sub = n.subscribe("semaphore", 1000, orderCallback);

And, as i said in the question, i have only boolean values.

check out the tutorial: http://wiki.ros.org/ROS/Tutorials/Wri... , your callback is also not correct.

@mig I have already checked it before posting. Can you help me with the code? If you can, of course. Thank you again.

What kind of message do you have? this needs to go in the callback function definition. See l.34 of the listener.cpp in the tutorial. Then, depending on the fields of the message, you can access this as shown in l.36 msg->data. But note, that the String.msg has a field called data. You need to

adapt this accordingly for whatever your message you use. Then, implement your logic in whatever way you like...

Thank you for your reply! I tried something like this:

void orderCallback(const std_msgs::Bool::ConstPtr& msg)
{
bool data;
msg->data;
if (data = 0)
{
chdir("/home/marco/catkin_ws/src/heart_rate_monitor");
system("get_hrv -R my_data_file.txt >doc.txt");
}
}

...i tried to adapt the callback of the tutorial to my case. Anyway, it doesn't seem to work. What i'm missing? P.S. is data == 0 in my real code, it was only a typo in the comment. Thank you again @mig