I want to find a way to get the ppid of a specific pid only using C low-level function. I know there is a way with bash commands, like "ps" etc, but I want to do it only in C language.
1 Answers
This should work as you expect. I used pid = 373 which is my current /usr/sbin/cron. It properly reports PPID of 1 (init):
% ./getppid
PPid = 1
Sample code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXBUF (BUFSIZ * 2)
int main () {
int ppid, pid = 373; // my current cron pid
char buf[MAXBUF];
char procname[32]; // Holds /proc/4294967296/status\0
FILE *fp;
snprintf(procname, sizeof(procname), "/proc/%u/status", pid);
fp = fopen(procname, "r");
if (fp != NULL) {
size_t ret = fread(buf, sizeof(char), MAXBUF-1, fp);
if (!ret) {
perror("Error reading file: ");
exit(1);
} else {
buf[ret++] = '\0'; // Terminate it.
}
}
fclose(fp);
char *ppid_loc = strstr(buf, "\nPPid:");
if (ppid_loc) {
ppid = sscanf(ppid_loc, "\nPPid:%d", &ppid);
if (!ppid || ppid == EOF) {
perror("scanf:");
exit(1);
}
printf("PPid = %d\n", ppid);
} else {
printf("Error finding PPid: in status\n");
exit(1);
}
}
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