int connect(int socket, const struct sockaddr *address,
socklen_taddress_len);
DESCRIPTION
The connect() function shall attempt to make a connection on
a socket. The function takes the following arguments:
socket
Specifies the file descriptor associated with the socket.
address
Points to a sockaddr structure containing the peer address.
The length and format of the address depend on the address
family of the socket.
address_len
Specifies the length of the sockaddr structure pointed to by
the address argument.
If the socket has not already been bound to a local address, connect()
shall bind it to an address which, unless the
socket's address family is AF_UNIX, is an unused local address.
If the initiating socket is not connection-mode, then connect()
shall set the socket's peer address, and no connection is
made. For SOCK_DGRAM sockets, the peer address identifies where all
datagrams are sent on subsequent send() functions, and limits
the remote sender for subsequent recv() functions. If address
is a null address for the protocol, the socket's peer
address shall be reset.
If the initiating socket is connection-mode, then connect()
shall attempt to establish a connection to the address
specified by the address argument. If the connection cannot
be established immediately and O_NONBLOCK is not set for the
file descriptor for the socket, connect() shall block for up
to an unspecified timeout interval until the connection is
established. If the timeout interval expires before the connection
is established, connect() shall fail and the connection
attempt shall be aborted. If connect() is interrupted by a signal
that is caught while blocked waiting to establish a
connection, connect() shall fail and set errno to [EINTR],
but the connection request shall not be aborted, and the
connection shall be established asynchronously.
If the connection cannot be established immediately and O_NONBLOCK
is set for the file descriptor for the socket,
connect() shall fail and set errno to [EINPROGRESS], but
the connection request shall not be aborted, and the
connection shall be established asynchronously. Subsequent calls to
connect() for the same socket, before the connection is
established, shall fail and set errno to [EALREADY].
When the connection has been established asynchronously, select()
and poll() shall indicate that the file descriptor for the socket
is ready for writing.
The socket in use may require the process to have appropriate privileges
to use the connect() function.
RETURN VALUE
Upon successful completion, connect() shall return 0; otherwise,
-1 shall be returned and errno set to indicate
the error.
ERRORS
The connect() function shall fail if:
EADDRNOTAVAIL
The specified address is not available from the local machine.
EAFNOSUPPORT
The specified address is not a valid address for the address family
of the specified socket.
EALREADY
A connection request is already in progress for the specified socket.
EBADF
The socket argument is not a valid file descriptor.
ECONNREFUSED
The target address was not listening for connections or refused the
connection request.
EINPROGRESS
O_NONBLOCK is set for the file descriptor for the socket and the connection
cannot be immediately established; the connection
shall be established asynchronously.
EINTR
The attempt to establish a connection was interrupted by delivery
of a signal that was caught; the connection shall be
established asynchronously.
EISCONN
The specified socket is connection-mode and is already connected.
ENETUNREACH
No route to the network is present.
ENOTSOCK
The socket argument does not refer to a socket.
EPROTOTYPE
The specified address has a different type than the socket bound to
the specified peer address.
ETIMEDOUT
The attempt to connect timed out before a connection was made.
If the address family of the socket is AF_UNIX, then connect()
shall fail if:
EIO
An I/O error occurred while reading from or writing to the file system.
ELOOP
A loop exists in symbolic links encountered during resolution of the
pathname in address.
ENAMETOOLONG
A component of a pathname exceeded {NAME_MAX} characters, or an entire
pathname exceeded {PATH_MAX} characters.
ENOENT
A component of the pathname does not name an existing file or the
pathname is an empty string.
ENOTDIR
A component of the path prefix of the pathname in address is
not a directory.
The connect() function may fail if:
EACCES
Search permission is denied for a component of the path prefix; or
write access to the named socket is denied.
EADDRINUSE
Attempt to establish a connection that uses addresses that are already
in use.
ECONNRESET
Remote host reset the connection request.
EHOSTUNREACH
The destination host cannot be reached (probably because the host
is down or a remote router cannot reach it).
EINVAL
The address_len argument is not a valid length for the address
family; or invalid address family in the sockaddr
structure.
ELOOP
More than {SYMLOOP_MAX} symbolic links were encountered during resolution
of the pathname in address.
ENAMETOOLONG
Pathname resolution of a symbolic link produced an intermediate result
whose length exceeds {PATH_MAX}.
ENETDOWN
The local network interface used to reach the destination is down.
ENOBUFS
No buffer space is available.
EOPNOTSUPP
The socket is listening and cannot be connected.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
If connect() fails, the state of the socket is unspecified.
Conforming applications should close the file descriptor and
create a new socket before attempting to reconnect.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
accept() , bind() , close() , getsockname()
, poll() , select() , send() , shutdown()
, socket() , the Base Definitions volume of IEEE Std 1003.1-2001,
<sys/socket.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
