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C Interface
AF_UNIX sockets only:
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
int connect (s, addr, addrlen)
int s;
struct sockaddr_un *addr;
int addrlen;
AF_INET sockets only:
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
int connect (s, addr, addrlen)
int s;
struct sockaddr_in *addr;
int addrlen;
Description
The parameter s is a socket descriptor. The
addr parameter is a pointer to a socket address structure.
This structure contains the address of a remote socket to which a connection
is established. The addrlen parameter specifies the size of
this address structure. Since the size of the socket address structure varies
between socket address families (16 bytes for AF_INET; 110 bytes for
AF_UNIX), the correct socket address structure should be used with
each address family (struct sockaddr_in for AF_INET,
struct sockaddr_un for AF_UNIX).
If the socket is of type SOCK_STREAM, then connect attempts
to contact the remote host in order to make a connection between the remote
socket (peer) and the local socket specified by s. The call
normally blocks until the connection completes. If non-blocking mode has been
enabled using the O_NONBLOCK or O_NDELAY fcntl
flags and the connection cannot be completed immediately, then connect
returns an error as described below. In these cases, the select call
can be used on this socket to determine when the connection has completed by
selecting it for writing.
The O_NONBLOCK and O_NDELAY flags are defined in
<fcntl.h> and are explained in the fcntl section. If
s is a SOCK_STREAM socket that is bound to the same
local address as another SOCK_STREAM socket and addr
is the same as the peer address of the other socket, connect returns
EADDRINUSE.
If the AF_INET socket does not already have a local address bound to
it (refer to the bind call), the
connect call also binds the socket to a local address chosen by the
system.
Stream sockets may successfully connect only once.
Return Value
If the call is successful, a 0 is returned. If it fails, a -1 is returned, and
an error code is stored in errno.
Errors
The following errors are returned by connect:
| Error Code |
Description |
| [EBADF]
| The argument s is not a valid file descriptor. |
| [ENOTSOCK] |
The argument s is a file descriptor for a file, not a
socket. |
| [EADDRNOTAVAIL] |
The specified address is not available on this machine, or the socket is
a tcp or udp socket and the zero port number is
specified. |
| [EAFNOSUPPORT] |
Addresses in the specified address family cannot be used with this socket.
For datagram sockets, the peer address is no longer maintained by the
system. |
| [EISCONN] |
The socket is already connected. |
| [EINVAL] |
The socket has already been shut down or has a listen active on
it, or addrlen is a bad value. |
| [ETIMEDOUT] |
Connection establishment timed out without establishing a connection.
The backlog parameter may be full. (Refer to the
listen call.) |
| [ECONNREFUSED] |
The attempt to connect was forcefully rejected. |
| [ENETUNREACH] |
The network is not reachable from this host. |
| [EADDRINUSE] |
The address is already in use. |
| [EFAULT] |
The addr parameter is not a valid pointer. |
| [EINPROGRESS] |
Non-blocking I/O is enabled using O_NONBLOCK or
O_NDELAY, and the connection cannot be completed immediately.
This is not a failure. |
| [ENOSPC] |
All available virtual circuits are in use. |
| [EOPNOTSUPP] |
A connect attempt was made on a socket type that does not
support this call. |
| [EINTR] |
The call was interrupted by a signal before a valid connection
arrived. |
MPE/iX Specific
The connect call is not supported for SOCK_DGRAM sockets on
the current release.
Author
UCB (University of California at Berkeley)
See Also
accept,
select,
socket,
getsockname,
fcntl
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