initiate a connection on a
s, const struct sockaddr
The parameter s is a socket. If it is of
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
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 use
only once; datagram sockets may use
multiple times to change their association. Datagram sockets may dissolve
the association by connecting to an invalid address, such as a null
If the connection or binding succeeds, 0 is returned. Otherwise a -1 is returned, and a more specific error code is stored in errno.
connect() call fails if:
- s is not a valid descriptor.
- s is not a socket.
- The specified address is not available on this machine.
- Addresses in the specified address family cannot be used with this socket.
- The socket is already connected.
- Connection establishment timed out without establishing a connection.
- A TCP connection with a local broadcast, the all-ones or a multicast address as the peer was attempted.
- The attempt to connect was forcefully rejected.
- The destination address specified an unreachable host.
- A connect was interrupted before it succeeded by the delivery of a signal.
- The network isn't reachable from this host.
- The address is already in use.
- The name parameter specifies an area outside the process address space.
- The socket is non-blocking and the connection cannot be completed
immediately. It is possible to
poll(2) for completion by selecting the socket for writing, and
SO_ERRORto check for error conditions.
- The socket is non-blocking and a previous connection attempt has not yet been completed.
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.
- A component of the path prefix is not a directory.
- A component of a pathname exceeded
NAME_MAXcharacters, or an entire pathname (including the terminating NUL) exceeded
- The named socket does not exist.
- Search permission is denied for a component of the path prefix.
- Write access to the named socket is denied.
- Too many symbolic links were encountered in translating the pathname.
- The file described by name is of a different type
than s. E.g., s may be of type
SOCK_STREAMwhereas name may refer to a socket of type
accept(2), getsockname(2), getsockopt(2), poll(2), select(2), socket(2)
connect() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”).
connect() system call first appeared