connect(2)connect(2)NAMEconnect - Connect two sockets
SYNOPSIS
#include <sys/socket.h>
int connect(
int socket,
const struct sockaddr *address,
socklen_t address_len );
[XNS4.0] The definition of the connect() function in XNS4.0 uses a
size_t data type instead of a socklen_t data type as specified in
XNS5.0 (the previous definition).
[Tru64 UNIX] The following definition of the connect() function does
not conform to current standards and is supported only for backward
compatibility (see standards(5) ). int connect(
int socket,
struct sockaddr *address,
int address_len );
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
connect(): XNS4.0, XNS5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
Specifies a file descriptor for the socket. Points to a sockaddr
structure, the format of which is determined by the domain and by the
behavior requested for the socket. The sockaddr structure is an overlay
for a sockaddr_in, sockaddr_un, sockaddr_in6, or sockaddr_storage
structure, depending on which of the supported address families is
active.
[Tru64 UNIX] If the compile-time option _SOCKADDR_LEN is
defined before the sys/socket.h header file is included, the
sockaddr structure takes 4.4BSD behavior, with a field for spec‐
ifying the length of the socket address. Otherwise, the default
4.3BSD sockaddr structure is used, with the length of the socket
address assumed to be 14 bytes or less.
If _SOCKADDR_LEN is defined, the 4.3BSD sockaddr structure is
defined with the name osockaddr. Specifies the length of the
sockaddr structure pointed to by the address parameter.
DESCRIPTION
The connect() function requests a connection between two sockets. The
kernel sets up the communications links between the sockets; both sock‐
ets must use the same address format and protocol.
The connect() function performs a different action for each of the fol‐
lowing types of initiating sockets: If the initiating socket is
SOCK_DGRAM, the connect() function establishes the peer address. The
peer address identifies the socket where all datagrams are sent on sub‐
sequent send() functions. It also identifies the socket from where
datagrams can be received; datagrams from other peer addresses are not
delivered. If address is a null address for the protocol, the socket's
peer address is reset.
No connections are made by this connect() function. If the ini‐
tiating socket is SOCK_STREAM, the connect() function attempts
to make a connection to the socket specified by the address
parameter. Each communication space interprets the address
parameter differently.
If the function fails for a connection mode socket, applications should
use the close() function to deallocate the socket and descriptor. If
attempting to reinitiate the connection, applications should create a
new socket.
If the connection cannot be established immediately, one of the follow‐
ing occurs: If the socket file descriptor is marked non-blocking, the
connect() function fails and sets errno to [EINPROGRESS]. However, the
connection request is not aborted; the connection will be established
asynchronously. If you make a call to connect() for the same socket
before the connection is established, the function fails and sets errno
to [EALREADY]. If the socket file descriptor is marked blocking, the
connect() function blocks for an unspecified amount of time until the
connection is established. If the timeout interval expires before the
connection is established, the function fails and aborts the connection
attempt. While blocked, if connect() is interrupted by a signal, it
fails and sets errno to [EINTR]. However, the connection request is not
aborted; the connection is established asynchronously.
RETURN VALUES
Upon successful completion, the connect() function returns a value of 0
(zero). Otherwise, a value of -1 is returned and errno is set to indi‐
cate the error.
ERRORS
If the connect() function fails, errno may be set to one of the follow‐
ing values: Search permission is denied for a component of the path
prefix; or write access to the named socket is denied.
[XNS4.0] This error applies to AF_UNIX sockets only. The spec‐
ified address is already in use. The specified address is not
available from the local machine. The addresses in the speci‐
fied address family cannot be used with this socket. A connec‐
tion request is already in progress for the specified socket.
The socket parameter is not valid. The attempt to connect was
rejected. The remote host reset the connection request. The
address parameter is not in a readable part of the user address
space. The specified host is not reachable. O_NONBLOCK is set
for the file descriptor for the socket and the connection cannot
be immediately established; the connection will be established
asynchronously. The connect() function was interrupted by a
signal while waiting for the connection to be established. The
connection establishment may continue asynchronously. The value
of the address_len parameter is invalid for the specified
address family; or the sa_family field in the socket address
structure is invalid for the protocol. For an AF_UNIX socket,
an I/O error occurred while reading from or writing to the file
system. The socket is already connected. For an AF_UNIX
socket, too many symbolic links were encountered in translating
the pathname in address. A component of the pathname exceeded
NAME_MAX characters, or an entire pathname exceeded PATH_MAX
characters. The local network connection is not operational.
No route to the network or host is present. Insufficient
resources are available in the system to complete the call. For
an AF_UNIX socket, a component of the pathname does not name an
existing file or the pathname is an empty string. The available
STREAMS resources were insufficient for the operation to com‐
plete. For an AF_UNIX socket, a component of the path prefix of
the pathname in address is not a directory. The socket parame‐
ter refers to a file, not a socket. The socket is listening and
cannot be connected. The specified address has a different type
than the socket bound to the specified peer address. The estab‐
lishment of a connection timed out before a connection was made.
[Tru64 UNIX] The socket is marked nonblocking, so the connec‐
tion cannot be immediately completed. The application program
can select the socket for writing during the connection process.
SEE ALSO
Functions: accept(2), bind(2), socket(2), getsockname(2), select(2),
send(2).
Standards: standards(5).
Network Programmer's Guide
connect(2)
