text: #include <postream.hpp>
  The postream class represents an input communication channel with the child process. The child process reads data from this stream and the parent process can write to it through the postream object. In other words, from the child's point of view, the communication channel is an input one, but from the parent's point of view it is an output one; hence the confusing postream name.
  postream objects cannot be copied because they own the file handle they use to communicate with the child and because they buffer data that flows through the communication channel.
  A postream object behaves as a std::ostream stream in all senses. The class is only provided because it must provide a method to let the caller explicitly close the communication channel.