Number of child processes in parent process C/C++, LINUX - c++

Question

I am programming in Linux using C/C++. I have a problem, i am trying to find a function or something in order to get number of child processes in parent process.
Help me please
Thanks

Answer 1

I'm not sure if POSIX defines a function for this, but you could always count them in a global variable yourself, just add 1 after every fork on the parent, and set it to 0 on the child..

Answer 2

int globalVariable = 0;
main() {
pid_t pID = fork();
if (pID == 0) { //child
globalVariable = 0;
cout << "Child Process" << end;
}
else if (pID < 0) { //failed to fork
cerr << "Failed to fork" << endl;
exit(1);
// Throw exception
}
else { // parent
cout << "Parent Process:";
++globalVariable;
}
}

Answer 3

Use the procfs : count the number of directories in /proc/[mypid]/task and you have the number of child processes started.
See proc(5) for more information.

Answer 4

You can use the 'ps' command with the --ppid option to list all the child processes and then count them using wc -l
ps --ppid | wc -l

Answer 5

Here is how you can do it in C++11, could easily be adapted to pre-C++11 or C if needed. You need to check every process in the system and see who it's parent is:
#include <dirent.h>
#include <unistd.h>
#include <limits.h>
#include <string>
#include <fstream>
using std::string;
using std::ifstream;
using std::to_string;
bool is_number(const string& s) {
string::const_iterator it = s.begin();
for (; it != s.end() && isdigit(*it); ++it) {
}
return !s.empty() && it == s.end();
}
int count_children(const pid_t pid) {
DIR* dir;
if ((dir = opendir("/proc"))) {
int num_children = 0;
for (struct dirent* ent; (ent = readdir(dir));) {
if (is_number(ent->d_name)) {
ifstream ifs(string("/proc/" + string(ent->d_name) + "/stat").c_str());
string word;
for (int i = 0; i < 4; ++i) {
ifs >> word;
}
if (word == to_string(pid)) {
++num_children;
}
}
}
closedir(dir);
return num_children;
}
perror("could not open directory");
return INT_MAX;
}
Another possible option in the parent process is to create a variable initialised to zero in the parent process and incrementing it every time you fork and decrementing every time you receive a SIGCHLD.