From Andrew Gierth ( email@example.com):
fcntl(soc, F_SETFL, O_NONBLOCK) is incorrect since it
clobbers all other file flags. Generally one gets away with it since
the other flags (
O_APPEND for example) don't really apply much to
sockets. In a similarly rough vein, you would use
fcntl(soc, F_SETFL, 0)
to go back to blocking mode.
To do it right, use
F_GETFL to get the current flags, set or clear the
O_NONBLOCK flag, then use
F_SETFL to set the flags.
And yes, the flag can be changed either way at will.
firstname.lastname@example.org) has outlined the following
procedure for using
connect(), which will allow you to
put a timeout on the
First, create the socket and put it into non-blocking mode, then call
connect(). There are three possibilities:
EINPROGRESS. The connection attempt has begun, but not yet completed.
If the connection succeeds:
select()as writable (and will also select as readable if data arrives)
If the connection fails:
getsockopt(SO_ERROR)to get the error status - but be careful; some systems return the error code in the result parameter of
getsockopt(), but others (incorrectly) cause the
getsockoptcall itself to fail with the stored value as the error.
Sample code that illustrates this can be found in the socket-faq
examples, in the file