GNU Info

(libc.info)Linked Channels

---

Next: Independent Channels Up: Stream/Descriptor Precautions

---

Enter node , (file) or (file)node

Linked Channels
---------------

   Channels that come from a single opening share the same file
position; we call them "linked" channels.  Linked channels result when
you make a stream from a descriptor using `fdopen', when you get a
descriptor from a stream with `fileno', when you copy a descriptor with
`dup' or `dup2', and when descriptors are inherited during `fork'.  For
files that don't support random access, such as terminals and pipes,
_all_ channels are effectively linked.  On random-access files, all
append-type output streams are effectively linked to each other.

   If you have been using a stream for I/O, and you want to do I/O using
another channel (either a stream or a descriptor) that is linked to it,
you must first "clean up" the stream that you have been using.  Note:
Cleaning Streams.

   Terminating a process, or executing a new program in the process,
destroys all the streams in the process.  If descriptors linked to these
streams persist in other processes, their file positions become
undefined as a result.  To prevent this, you must clean up the streams
before destroying them.