linux: programmatically get parent pid of another process?

Question

I tried google, but found getppid() which gets the parent pid of the current process.

I need something like getppid(some_other_pid), is there such a thing? Basically takes the pid of some process and returns the parent process' pid.

Answer 1

pstree knows how to do it, maybe look at the source and see how it does it

Answer 2

I think the simplest thing would be to open "/proc" and parse the contents.

You'll find the ppid as the 4th parameter of /proc/pid/stat

Answer 3

You can have a look at sysctl() system call and this link.