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Top Forums Programming Automatic port selection using C in Linux? Post 302490911 by GeorgeCostanza on Wednesday 26th of January 2011 05:59:13 AM
Old 01-26-2011
Question Automatic port selection using C in Linux?

Hi

What would be the correct way to get the port number for a free port, using C in Linux?

I've tried to create() and bind() a socket without specifying the port, and that seems to work in some cases (using gcc, and some Linux dist).
When compiling with the Intel Icc64 compiler I suddenly had to do a "dummy send" with the created socket to get a port != 0.
Then, when using that technique on mashines running Slackware 13, it doesn't work. I just get the port to be 0.

So, is there a "correct" way to do this?
I'm trying to find out free port numbers that clients can use to receive messages from a server, and I would like to retreive them before actually sending anything between server/client.

Help, please...

/GC
 

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efax-gtk-socket-client(1)				      General Commands Manual					 efax-gtk-socket-client(1)

NAME
efax-gtk-socket-client - a client of efax-gtk to work with lpd/lprng SYNOPSIS
efax-gtk-socket-client [hostname] [port] DESCRIPTION
This program enables lpd/lprng to access the efax-gtk socket server. Meaning the user can send faxes to a printer, which will ack as a fax. It takes two arguments - first a hostname to connect to, and secondly a port number at that hostname to connect to. All efax-gtk-socket- client does is to read from standard input (in this case from lpd/lprng) and passes it to a socket at the hostname and port number passed as arguments to it (namely the hostname of the computer efax-gtk is running on - normally you would specify localhost - and the port number of the socket). fax: :sd=/var/spool/fax: :mx#0: :sh: :lp=/dev/null: :if=/var/spool/fax/efax-gtk-faxfilter: This will cause a printer by the name of "fax" to be available, which (if printed to) will send the file to the efax-gtk socket server. If you set efax-gtk to listen on a port other than port 9900, you will need to amend the file /var/spool/fax/efax-gtk-faxfilter by hand to specify the correct port number on which efax-gtk is listening. Don't forget to restart the lpd printer daemon after amending /etc/printcap. OPTIONS
[ hostname ] - The name of the host to listen to. Usually should be locahlhost. [ port ] - the port number to listen to on the [ hostname ]. SEE ALSO
efax(1), efax-gtk(1). AUTHOR
efax-gtk-socket-client was written by Chris Vine <chris@cvine.freeserve.co.uk>. This manual page was written by Lior Kaplan <kaplan@debian.org>, for the Debian project (but may be used by others). July 18, 2006 efax-gtk-socket-client(1)
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