This is a basic example of inter-process communication
using fork() and pipe() in C++

Includes an example of creating a C++ stream from a file descriptor
and how to read/write from/to it using << and >> operators

Needs GCC's libstdc++ and a POSIX environment

Usage:
	$ make
	$ ./parent

Output:
	Parent: I'll send the child a message.
	Parent: Child just said through stdout:
		"Program: I've received: 'Hello Child!'"
	Parent: Child just said through stderr:
		"Program: This is the error stream!"


The scenario is: A parent process wants to handle another program’s
input and output streams, a process-level wrapper.

So the example is: A parent process forks into another child
process. The parent sends the child a message, the child receives it
and outputs it to the parent to show the communication works just
fine.

The forked process calls the program we want to control. Which in this
case is the easiest C++ program ever: Just reads a line from the
standard input and outputs a message containing the line just read
through the standard output. In addition, another message is sent
through the standard error stream.

Further explanation:
https://blog.eldruin.com/inter-process-communication-pipe-fork-cpp-stl-like-streams/

Resources:
     YoLinux Tutorial: Fork, Exec and Process control
     Beginning Linux programming, Matthew & Stones, Wrox Press
     The GNU C Library manual
     The GNU C++ Library manual
     fileno(3) on C++ Streams: A Hacker's Lament, Richard B. Kreckel


Author: Diego Barrios Romero
Public domain Copyleft 2011