Short program to show forking in C++ and how to create zombie process.

fork-cpp-example.cpp

#include <iostream>
#include <unistd.h>

int main()
{
	std::cout << "------ program started ------" << std::endl;

	int counter = 0;
	pid_t pid = fork();

	/*
	* fork() returns -1 if it fails, 
	* and if it succeeds, it returns the forked child's pid in the parent,
	* and 0 in the child. So if (fork() != 0) tests whether it's the parent process.
	*/
	if (pid == 0) {
		// child process
		for (int i = 0; i < 5; ++i) {
			//sleep(5);
			counter += 1;
			std::cout << "child process: counter = " << counter << std::endl;
		}

		/* 
		* to create zombie process uncomment this line and the sleep(30) in the parent branch -> 
		* you can chack it with ps aux | grep <process name> -> Z will indicate it is a zombie
		*/
		// exit(0);
	} else if (pid > 0) {
		//sleep(30);
		// parent process
		for(int i = 0; i < 5; ++i) {
			sleep(5);
			counter += 5;
			std::cout << "parent process: counter = " << counter << std::endl;
		}
	} else {
		// fork failed
		std::cout << "fork() failed" << std::endl;
		return 1;
	}

	std::cout << "------ end of program pid = " << pid << "------" << std::endl;
	return 0;
}