NAME
connect —
initiate a connection on a
socket
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/socket.h>
int
connect(
int
s,
const struct sockaddr
*name,
socklen_t
namelen);
DESCRIPTION
The parameter
s is a socket. If it is of type
SOCK_DGRAM
, this call specifies the peer with which
the socket is to be associated; this address is that to which datagrams are to
be sent, and the only address from which datagrams are to be received. If the
socket is of type
SOCK_STREAM
, this call attempts to
make a connection to another socket. The other socket is specified by
name, which is an address in the communications space of
the socket.
namelen indicates the amount of space
pointed to by
name, in bytes. Each communications space
interprets the
name parameter in its own way. 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 an invalid address, such as a null address.
If a
connect() call is interrupted by a signal, it will return
with errno set to
EINTR
and the connection attempt
will proceed as if the socket was non-blocking. Subsequent calls to
connect() will set errno to
EALREADY
.
RETURN VALUES
If the connection or binding succeeds, 0 is returned. Otherwise a -1 is
returned, and a more specific error code is stored in
errno.
ERRORS
The
connect() call fails if:
-
-
- [
EBADF
]
- s is not a valid descriptor.
-
-
- [
ENOTSOCK
]
- s is a descriptor for a file, not a
socket.
-
-
- [
EADDRNOTAVAIL
]
- The specified address is not available on this
machine.
-
-
- [
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.
-
-
- [
ENETUNREACH
]
- The network isn't reachable from this host.
-
-
- [
EADDRINUSE
]
- The address is already in use.
-
-
- [
EFAULT
]
- The name parameter specifies an area
outside the process address space.
-
-
- [
EINPROGRESS
]
- The socket is non-blocking and the connection cannot be
completed immediately. It is possible to
select(2) or
poll(2) for completion by
selecting or polling the socket for writing. The success or failure of the
connect operation may be determined by using
getsockopt(2) to read
the socket error status with the
SO_ERROR
option
at the SOL_SOCKET
level. The returned socket error
status is zero on success, or one of the error codes listed here on
failure.
-
-
- [
EALREADY
]
- Either the socket is non-blocking mode or a previous call
to connect() was interrupted by a signal, and the
connection attempt has not yet been completed.
-
-
- [
EINTR
]
- The connection attempt was interrupted by a signal.
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 is not a directory.
-
-
- [
ENAMETOOLONG
]
- A component of a pathname exceeded
{
NAME_MAX
} characters, or an entire path name
exceeded {PATH_MAX
} characters.
-
-
- [
ENOENT
]
- The named socket does not exist.
-
-
- [
EACCES
]
- Search permission is denied for a component of the path
prefix, or write access to the named socket is denied.
-
-
- [
ELOOP
]
- Too many symbolic links were encountered in translating the
pathname.
SEE ALSO
accept(2),
getsockname(2),
getsockopt(2),
poll(2),
select(2),
socket(2)
HISTORY
The
connect() function call appeared in
4.2BSD.