connect(2) connect(2)
NAME [Toc] [Back]
connect - initiate a connection on a socket
SYNOPSIS [Toc] [Back]
#include <sys/socket.h>
AF_CCITT only [Toc] [Back]
#include <x25/x25addrstr.h>
AF_INET, AF_INET6 and AF_VME_LINK only
#include <netinet/in.h>
AF_UNIX only [Toc] [Back]
#include <sys/un.h>
int connect(int s, const void *addr, int addrlen);
_XOPEN_SOURCE_EXTENDED only (UNIX 98)
int connect(int s, const struct sockaddr *addr, socklen_t addrlen);
Obsolescent _XOPEN_SOURCE_EXTENDED only (UNIX 95) [Toc] [Back]
int connect(int s, const struct sockaddr *addr, size_t addrlen);
DESCRIPTION [Toc] [Back]
The connect() function initiates a connection on a socket.
s is a socket descriptor.
addr is a pointer to a socket address structure containing the address
of a remote socket to which a connection is to be established.
addrlen is the size of this address structure. Since the size of the
socket address structure varies among socket address families, the
correct socket address structure should be used with each address
family (for example, struct sockaddr_in for AF_INET and AF_VME_LINK,
struct sockaddr_in6 for AF_INET6, and struct sockaddr_un for AF_UNIX).
Typically, the sizeof() function is used to pass this value (for
example, sizeof(struct sockaddr_in)).
If the socket is of type SOCK_DGRAM, connect() specifies the peer
address to which messages are to be sent, and the call returns
immediately. Furthermore, this socket can only receive messages sent
from this address.
If the socket is of type SOCK_STREAM, connect() attempts to contact
the remote host to make a connection between the remote socket (peer)
and the local socket specified by s. The call normally blocks until
the connection completes. If nonblocking mode has been enabled with
the O_NONBLOCK or O_NDELAY fcntl() flags or the FIOSNBIO ioctl()
request and the connection cannot be completed immediately, connect()
returns an error as described below. In these cases, select() can be
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connect(2) connect(2)
used on this socket to determine when the connection has completed by
selecting it for writing.
The connect() system call may complete if remote program has a pending
listen() even though remote program had not yet issued an accept()
system call.
O_NONBLOCK and O_NDELAY are defined in <sys/fcntl.h> and explained in
fcntl(2), fcntl(5), and socket(7). FIOSNBIO is defined in
<sys/ioctl.h> and explained in ioctl(2), ioctl(5), and socket(7).
If s is a SOCK_STREAM socket that is bound to the same local address
as another SOCK_STREAM socket, connect() returns [EADDRINUSE] if addr
is the same as the peer address of that other socket. This situation
can only happen if the SO_REUSEADDR option has been set on s, which is
an AF_INET or AF_INET6 socket (see getsockopt(2)).
If the AF_INET or AF_INET6 socket does not already have a local
address bound to it (see bind(2)), connect() also binds the socket to
a local address chosen by the system.
An AF_VME_LINK socket always binds the socket to a local address
chosen by the system.
Generally, stream sockets may successfully connect only once; datagram
sockets may use connect() multiple times to change the peer address.
For datagram sockets, a side effect of attempting to connect to some
invalid address (see ERRORS below) is that the peer address is no
longer maintained by the system. An example of an invalid address for
a datagram socket is addrlen set to 0 and addr set to any value.
AF_CCITT Only [Toc] [Back]
Use the x25addrstr struct for the address structure. The caller must
know the X.121 address of the DTE to which the connection is to be
established, including any subaddresses or protocol IDs that may be
needed. If address-matching by protocol ID, specify the protocol ID
with the X25_WR_USER_DATA ioctl() call before issuing the connect()
call.
DEPENDENCIES [Toc] [Back]
AF_CCITT
The SO_REUSEADDR option to setsockopt() is not supported for sockets
in the AF_CCITT address family.
RETURN VALUE [Toc] [Back]
connect() returns the following values:
0 Successful completion.
-1 Failure. errno is set to indicate the error.
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connect(2) connect(2)
ERRORS [Toc] [Back]
If connect() fails, errno is set to one of the following values.
[EADDRINUSE] The specified address is already in use.
For datagram sockets, the peer address
is no longer maintained by the system.
[EADDRNOTAVAIL] The specified address is not available
on this machine, or the socket is a
TCP/UDP socket and the zero port number
is specified.
For datagram sockets, the peer address
is no longer maintained by the system.
[EAFNOSUPPORT] The specified address is not a valid
address for the address family of this
socket.
For datagram sockets, the peer address
is no longer maintained by the system.
[EALREADY] Nonblocking I/O is enabled with
O_NONBLOCK, O_NDELAY, or FIOSNBIO, and a
previous connection attempt has not yet
completed.
[EBADF] s is not a valid file descriptor.
[ECONNREFUSED] The attempt to connect was forcefully
rejected.
[EFAULT] addr is not a valid pointer.
[EINPROGRESS] Nonblocking I/O is enabled using
O_NONBLOCK, O_NDELAY, or FIOSNBIO, and
the connection cannot be completed
immediately. This is not a failure.
Make the connect() call again a few
seconds later. Alternatively, wait for
completion by calling select() and
selecting for write.
[EINTR] The connect was interrupted by a signal
before the connect sequence was
complete. The building of the
connection still takes place, even
though the user is not blocked on the
connect() call.
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connect(2) connect(2)
[EINVAL] The socket has already been shut down or
has a listen() active on it; addrlen is
a bad value; an attempt was made to
connect() an AF_UNIX socket to an NFSmounted
(remote) name; the X.121 address
length is zero, negative, or greater
than 15 digits.
For datagram sockets, if addrlen is a
bad value, the peer address is no longer
maintained by the system.
[EISCONN] The socket is already connected.
[ENETDOWN] The X.25 interface specified in the addr
struct was found but was not in the
initialized state. x25ifname field name
is an interface which has been shut down
or never initialized or suffered a power
failure which erased its state
information.
[ENETUNREACH] The network is not reachable from this
host.
For AF_CCITT only: X.25 Level 2 is down.
The X.25 link is not working: wires
might be broken, connections are loose
on the interface hoods at the modem, the
modem failed, or noise interfered with
the line for an extremely long period of
time.
[ENOBUFS] No buffer space is available. The
connect() has failed.
[ENOMEM] No memory is available. The connect()
has failed.
[ENOPROTOOPT] The remote system or an intermediate
system in the communications path does
not support a protocol option sent by
the local system. This option may have
been set using a getsockopt() or
setsockopt() call, or set as a system
parameter.
[ENODEV] The x25ifname field refers to a
nonexistent interface.
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connect(2) connect(2)
[ENOSPC] All available virtual circuits are in
use.
[ENOTSOCK] s is a valid file descriptor, but it is
not a socket.
[EOPNOTSUPP] The socket referenced by s does not
support connect(). With X.25 an attempt
was made to issue a connect() call on a
listen() socket.
[ETIMEDOUT] Connection establishment timed out
without establishing a connection. One
reason could be that the connection
requests queue at the remote socket may
be full (see listen(2)).
WARNINGS [Toc] [Back]
IPv6 is supported on HP-UX 11i Version 1.0, with the optional IPv6
software installed. Currently, IPv6 is not supported on systems
running HP-UX 11i Version 1.6.
OBSOLESCENCE [Toc] [Back]
Currently, the socklen_t and size_t types are the same size. This is
compatible with both the UNIX 95 and UNIX 98 profiles. However, in a
future release, socklen_t might be a different size, but that should
not adversely affect application behavior in this case. Applications
may use socklen_t now. But applications that need to be portable to
the UNIX 95 profile should follow the X/Open specification (see
xopen_networking(7)).
FUTURE DIRECTION [Toc] [Back]
Currently, the default behavior is the HP-UX BSD Sockets; however, it
might be changed to X/Open Sockets in a future release. At that time,
any HP-UX BSD Sockets behavior that is incompatible with X/Open
Sockets might be obsoleted. Applications that conform to the X/Open
specification now will avoid migration problems (see
xopen_networking(7)).
AUTHOR [Toc] [Back]
connect() was developed by HP and the University of California,
Berkeley.
SEE ALSO [Toc] [Back]
accept(2), getsockname(2), select(2), socket(2), thread_safety(5),
socket(7), xopen_networking(7).
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