Question

I am currently developing a modular framework using shared memory in C & C++.
The goal is to have independent programs in both C and C++, talk to each other through shared memory.

E.g. one program is responsible for reading a GPS and another responsible for processing the data from several sensors.

A master program will start all the slave programs
(currently i am using fp = popen(./slave1/slave1,"r"); to do this) and then make shared memory segments that each slave can connect to.
The thought behind this is that if a slave dies, it can be revived by the master and reconnect to the same shared memory segment.
Slaves can also be exchanged during runtime (e.g. switch one GPS with another).

The problem is that I spawn the slave via popen, and pass the shared memory ID to the slave. Via the pipe the slave transmits back the size needed.
After this is done i want to reroute the slave’s pipe to terminal to display debug messages and not pass through the master.

Suggestions are greatly appreciated, as well as other solutions to the issue.
The key is to have some form of communication prior to setting up the shared memory.

Answer 1

Pipes are not reroutable — they go where they go when they were created. What you need to do is have the slave close the pipe when its done with it, and then reopen its stdout elsewhere. If you always want output to the terminal, you can use freopen("/dev/tty", "w", stdout), but then it will always go to the terminal — you can’t redirect it anywhere else.