How to call node publisher from C function

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Hello, guys!

I'm using ROS2 Foxy with Ubuntu 18.04. I successfully integrated my C application code into ROS2 node but there is one single thing left to be done. Namely, I have an asynchronous C callback function that is called every time I receive new data over USB. I need to use Node publisher to publish those data through the topic to other subscriber nodes.

How can I do it from my callback function located in C file? How can I call my node's publisher from there? Is this a question of mixing C and C++? Any experience to share with me?

Thanks in advance for your time and efforts. Sincerely, Bojan.