macos - How to programatically get uid from pid in osx using c++?

Question

Given a pid, I want to find the owner of the process (as uid). Is there a way to get this in osx (or any unix) using C++?

Google didn't help. 'ps' is able to do it; so I assume there should be a way to get it programatically.

Answer 1

Solution from Indhu helped me on my way, so I would like to post my own.

UID from PID with pure C:

#include <sys/sysctl.h>

uid_t uidFromPid(pid_t pid)
{
    uid_t uid = -1;

    struct kinfo_proc process;
    size_t procBufferSize = sizeof(process);

    // Compose search path for sysctl. Here you can specify PID directly.
    const u_int pathLenth = 4;
    int path[pathLenth] = {CTL_KERN, KERN_PROC, KERN_PROC_PID, pid};

    int sysctlResult = sysctl(path, pathLenth, &process, &procBufferSize, NULL, 0);

    // If sysctl did not fail and process with PID available - take UID.
    if ((sysctlResult == 0) && (procBufferSize != 0))
    {
        uid = process.kp_eproc.e_ucred.cr_uid;
    }

    return uid;
}

No excess allocation, no loops.