Function waitpid 

pub fn waitpid(pid: i32) -> Result<(), i32>

Wait for process to change status see wait(2)

Errors

returns -1 if error

Example:

use fork::{waitpid, Fork};
use std::process::Command;

fn main() {
 match fork::fork() {
    Ok(Fork::Parent(pid)) => {

        println!("Child pid: {pid}");

        match waitpid(pid) {
            Ok(_) => println!("Child existed"),
            Err(_) => eprintln!("Failted to wait on child"),
        }
    }
    Ok(Fork::Child) => {
        Command::new("sleep")
            .arg("1")
            .output()
            .expect("failed to execute process");
    }
    Err(_) => eprintln!("Failed to fork"),
 }
}