getppidbypid

#include <stdio.h>
#include <unistd.h>

int getppidbypid(int pid)
{
    int p, pp;
    FILE *F;
    char buf[256];

    sprintf(buf, "ps -o pid,ppid -p %d", pid);

    F = popen(buf, "r");
    if (!F) {
        /* Can not run ps */
        return -1;
    }

    while (!feof(F)) {
        if (!fgets(buf, sizeof(buf), F)) {
            pclose(F);
            return -1;
        }

        if (sscanf(buf, "%d %d", &p, &pp) > 0) {
            if (p == pid) {
                pclose(F);
                return pp;
            }
        }
    }

    pclose(F);

    return -1; /* Not found */
}

int main(int argc, char *argv[])
{
    int i;
    int p;

    for (i = 1; i < argc; i++) {
        p = atoi(argv[i]);

        printf("[%d] -> [%d]\n", getppidbypid(p), p);
    }

    return 0;
}