function for getting pid of "any" process

nice_indian · 01-12-2005, 05:11 AM

Hi,
i want to get process id of the parent of some process whose pid is known.
whats the c function for this. getppid() gives parent pid of current process only. Is there any way to get ancestor id.

Please help!!! Thanx in advance.
I can get ppid of any process using "ps -el | grep pid" but i want c function.

Hko · 01-12-2005, 07:00 AM

AFAIK there's no standard function call available to do this. You need to use the /proc filesystem to read it. Here's a quick program that uses its own function to get its parent pid from /proc.

Code:

#include <sys/types.h>
#include <unistd.h>

#define MAXPIDLEN 10
#define MAXPROCPATHLEN (MAXPIDLEN + 11)


pid_t parentpidof(pid_t pid)
{
    pid_t ppid;
    char procpath[MAXPROCPATHLEN];
    FILE *procstat;

    snprintf(procpath, MAXPROCPATHLEN, "/proc/%u/stat", pid);
    procstat = fopen(procpath, "r");
    if (procstat < 0) {
        perror("fopen(procstat)");
        return 0;
    }
    fscanf(procstat, "%*d %*s %*c %u", &ppid);
    fclose(procstat);
    return ppid;
}


int main()
{
    pid_t mypid;
    pid_t myparentpid;

    mypid = getpid();
    myparentpid = parentpidof(mypid);
    printf("%u\n", myparentpid);
    return 0;
}

nice_indian · 01-12-2005, 09:54 AM

Thanx a lot sir, This is exactly what i wanted.