boost/boost_1_91_0/libs/process/doc/reference/pid.adoc

pid.hpp

//An integral type representing a process id.
typedef implementation_defined pid_type;

// Get the process id of the current process.
pid_type current_pid();

// List all available pids.
std::vector<pid_type> all_pids(boost::system::error_code & ec);
std::vector<pid_type> all_pids();

// return parent pid of pid.
pid_type parent_pid(pid_type pid, boost::system::error_code & ec);
pid_type parent_pid(pid_type pid);

// return child pids of pid.
std::vector<pid_type> child_pids(pid_type pid, boost::system::error_code & ec);
std::vector<pid_type> child_pids(pid_type pid);