connect() — Connect a socket

X/Open:

#define _XOPEN_SOURCE_EXTENDED 1
#include <sys/socket.h>

int connect(int socket, const struct sockaddr *address, socklen_t address_len);

Berkeley sockets:

#define _OE_SOCKETS
#include <sys/types.h>
#include <sys/socket.h>

int connect(int socket, struct sockaddr *address, int address_len);

Servers in the AF_INET domain: If the server is in the AF_INET domain, the format of the name buffer is expected to be sockaddr_in, as defined in the include file netinet/in.h.

struct in_addr
{
        ip_addr_t s_addr;
};

 struct sockaddr_in {
     unsigned char  sin_len;
     unsigned char  sin_family;
     unsigned short sin_port;
     struct in_addr sin_addr;
     unsigned char  sin_zero[8];

};

Servers in the AF_INET6 domain: If the server is in the AF_INET6 domain, the format of the name buffer is expected to be sockaddr_in6, as defined in the netinet/in.h:

 struct sockaddr_in6 {
     uint8_t char    sin6_len;
     sa_family_t     sin6_family;
     in_port_t       sin6_port;
     uint32_t        sin6_flowinfo;
     struct in6_addr sin6_addr;
     uint32_t        sin6_scope_id;
];

Servers in the AF_UNIX domain: If the server is in the AF_UNIX domain, the format of the name buffer is expected to be sockaddr_un, as defined in the include file un.h.

 struct sockaddr_un {
    unsigned char  sun_len;
    unsigned char  sun_family;
             char  sun_path[108];        /* path name */
};

Special behavior for C++: To use this function with C++, you must use the _XOPEN_SOURCE_EXTENDED 1 feature test macro.

If unsuccessful, connect() returns -1 and sets errno to one of the following values:

Error Code

Description

EADDRNOTAVAIL

The specified address is not available from the local machine.

EAFNOSUPPORT

The address family is not supported.

EALREADY

The socket descriptor socket is marked nonblocking, and a previous connection attempt has not completed.

EBADF

The socket parameter is not a valid socket descriptor.

ECONNREFUSED

The connection request was rejected by the destination host.

EFAULT

Using address and address_len would result in an attempt to copy the address into a portion of the caller's address space to which data cannot be written.

EINTR

The attempt to establish a connection was interrupted by delivery of a signal that was caught. The connection will be established asynchronously.

EINVAL

The address_len parameter is not a valid length.

EIO

There has been a network or a transport failure.

EISCONN

The socket descriptor socket is already connected.

ENETUNREACH

The network cannot be reached from this host.

ENOTSOCK

The descriptor refers to a file, not a socket.

EOPNOTSUPP

The socket parameter is not of type SOCK_STREAM.

EPERM

connect() caller was attempting to extract a user's identity and the caller's process was not verified to be a server. To be server-verified, the caller's process must have permission to the BPX.SERVER profile (or superuser and BPX.SERVER is undefined) and have called either the __passwd() or pthread_security_np() services before calling connect() to propagate identity.

EPROTOTYPE

The protocol is the wrong type for this socket.

ETIMEDOUT

The connection establishment timed out before a connection was made.

The following are for AF_UNIX only:

Error Code

Description

EACCES

Search permission is denied for a component of the path prefix, or write access to the named socket is denied.

EIO

An I/O error occurred while reading from or writing to the file system.

ELOOP

Too many symbolic links were encountered in translating the path name in address.

ENAMETOOLONG

A component of a path name exceeded NAME_MAX characters, or an entire path name exceeded PATH_MAX characters.

ENOENT

A component of the path name does not name an existing file or the path name is an empty string.

ENOTDIR

A component of the path prefix of the path name in address is not a directory.

The following are examples of the connect() call. The Internet address and port must be in network byte order. To put the port into network byte order, the htons() utility routine is called to convert a short integer from host byte order to network byte order. The address field is set using another utility routine, inet_addr(), which takes a character string representing the dotted-decimal address of an interface and returns the binary Internet address representation in network byte order. Finally, it is a good idea to zero the structure before using it to ensure that the name requested does not set any reserved fields. These examples could be used to connect to the servers shown in the examples listed with the call, bind() — Bind a name to a socket.

int s;
struct sockaddr_in inet_server;
struct sockaddr_un unix_server;
int rc;
int connect(int s, struct sockaddr *name, int namelen);

/* Connect to server bound to a specific interface in the 
Internet domain */
/* make sure the sin_zero field is cleared */
memset(&inet_server, 0, sizeof(inet_server));
inet_server.sin_family = AF_INET;
inet_server.sin_addr.s_addr = inet_addr("129.5.24.1"); 
/* specific interface */
inet_server.sin_port = htons(1024);
⋮
rc = connect(s, (struct sockaddr *) &inet_server, 
sizeof(inet_server));

/* Connect to a server bound to a name in the UNIX domain */
/* make sure the sunix_addr, sunix_port, sunix_nodeid fields are cleared
*/
memset(&unix_server, 0, sizeof(unix_server));
unix_server.sun_family = AF_UNIX;
strncpy(unix_server.sun_path, "mysocket");
unix_server.sun_len = sizeof(unix_server.sun_len);
strncpy(mvsservername.sunix_name, "APPL    ", 8);
⋮
rc = connect(s, (struct sockaddr *) 
&unix_server, sizeof(unix_server));