Is there any way in C to know how many processes there are with the same pgid?

Question

I want to know if there is any function in C (Linux) to know how many processes are there with a certain pgid. For example:

  PID  PGID  PPID COMMAND
 9024 27852 27855 ./asdf
 9033 27852 27856 ./asdf
 9035 27852 27854 ./asdf
 9037 27852 27856 ./asdf
 9039 27852 27854 ./asdf

If I have these processes, the function(27852) will return 5 processes.

Answer 1

Succinctly, No — AFAICT.

POSIX provides a number of functions for manipulating process groups, but not an interrogation function to find out which processes belong to a specified process group. This is consistent with other system calls; there are no system calls that return fully open-ended lists of 'items of interest'.

• getpgid()
• setpgid()
• getpgrp()
• setpgrp()
• killpg()
• posix_spawnattr_getpgroup()
• posix_spawnattr_setpgroup()
• tcgetpgrp()
• tcsetpgrp()

You can search through the Linux manual pages at http://man7.org/linux/man-pages:

• Section 2 (system calls): http://man7.org/linux/man-pages/man2/
• Section 3 (library functions): http://man7.org/linux/man-pages/man3/

The same names as in POSIX turn up; no other relevant looking entries turn up.