How to run a program in a separate process in linux in C ++, get its PID and transfer the contents of the file to the stdin of the process?

Question

linux

The someProgram program is only available in binary form.
I tried
popen("cat ./someFile | ./someProgram &")
but instead of PID it gives the result of someProgram.
The PID is needed to kill someProgram if it takes too long to run.

Answer 1

fork(), system(), getpid()