connect - initiate a connection on a socket
connect(int s, caddr_t name, int namelen);
The parameter s is a socket. If it is of type SOCK_DGRAM, connect()
specifies the peer with which the socket is to be associated; this
address is the address to which datagrams are to be sent if a receiver is
not explicitly designated; it is the only address from which datagrams
are to be received. If the socket s is of type SOCK_STREAM, connect()
attempts to make a connection to another socket. The other socket is
specified by name. name is an address in the communications space of the
socket. Each communications space interprets the name parameter in its
own way. If s is not bound, then it will be bound to an address selected
by the underlying transport provider. Generally, stream sockets may
successfully connect() only once; datagram sockets may use connect()
multiple times to change their association. Datagram sockets may
dissolve the association by connecting to a null address.
If the connection or binding succeeds, then 0 is returned. Otherwise a
-1 is returned and a more specific error code is stored in errno.
The call fails if:
EBADF s is not a valid descriptor.
ENOTSOCK s is a descriptor for a file, not a socket.
EINVAL namelen is not the size of a valid address for the
specified address family.
EADDRNOTAVAIL The specified address is not available on the remote
EAFNOSUPPORT Addresses in the specified address family cannot be
used with this socket.
EISCONN The socket is already connected.
ETIMEDOUT Connection establishment timed out without
establishing a connection.
ECONNREFUSED The attempt to connect was forcefully rejected. The
calling program should close(2) the socket
descriptor, and issue another socket(3N) call to
obtain a new descriptor before attempting another
ENETUNREACH The network is not reachable from this host.
EADDRINUSE The address is already in use.
EINPROGRESS The socket is non-blocking and the connection cannot
be completed immediately. It is possible to
select(3N) for completion by selecting the socket for
writing. However, this is only possible if the
socket STREAMS module is the topmost module on the
protocol stack with a write service procedure. This
will be the normal case.
EALREADY The socket is non-blocking and a previous connection
attempt has not yet been completed.
EINTR The connection attempt was interrupted before any
data arrived by the delivery of a signal.
ENOTSOCK The file referred to by name is not a socket.
EPROTOTYPE The file referred to by name is a socket of a type
other than type s (for example, s is a SOCK_DGRAM
socket, while name refers to a SOCK_STREAM socket).
ENOSR There were insufficient STREAMS resources available
to complete the operation.
The following errors are specific to connecting names in the UNIX domain.
These errors may not apply in future versions of the UNIX IPC domain.
ENOTDIR A component of the path prefix of the pathname in
name is not a directory.
ENOENT A component of the path prefix of the pathname in
name does not exist.
ENOENT The socket referred to by the pathname in name does
EACCES Search permission is denied for a component of the
path prefix of the pathname in name.
ELOOP Too many symbolic links were encountered in
translating the pathname in name.
EIO An I/O error occurred while reading from or writing
to the file system.
accept(3N), connect(3N), getsockname(3N), socket(3N)
The type of address structure passed to connect() depends on the address
family. UNIX domain sockets (address family AF_UNIX) require a struct
socketaddr_un as defined in sys/un.h; Internet domain sockets (address
family AF_INET) require a struct sockaddr_in as defined in netinet/in.h.
Other address families may require other structures. Use the structure
appropriate to the address family; cast the structure address to a
generic caddr_t in the call to connect() and pass the size of the
structure in the length argument.
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