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C Interface
#include <sys/types.h>
#include <sys/socket.h>
int socket (af, type, protocol)
int af, type, protocol;
Description
The socket call creates an endpoint for communication and returns a
descriptor. The socket descriptor returned is used in all subsequent
socket-related system calls.he af parameter specifies an
address family to be used to interpret addresses in later operations that
specify the socket. These address families are defined in the include file
<sys/socket.h>. The only currently supported address families
are as follows:
AF_INET (DARPA Internet addresses)
AF_UNIX (directory path names on a local node)
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NOTE: If you do not have a supported networking link product
installed on your system and you attempt to use the address family
AF_INET, then the EAFNOSUPPORT error is returned.
The AF_UNIX address family can be used to create socket connections
without requiring a networking link product to be installed.
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The type parameter specifies the communication semantics for
the socket. Currently defined types are as follows:
SOCK_STREAM
SOCK_DGRAM
A SOCK_STREAM type provides sequenced, reliable, two-way,
connection-based byte streams. A SOCK_DGRAM socket supports datagrams,
which are connection-less, unreliable messages of a fixed, typically small,
maximum length.
The protocol parameter specifies a particular protocol to be
used with the socket. The protocol number to use depends on the communication
domain in which communication is to take place. (Refer to the chapter on name
services routines.) Protocol can be supplied as zero, in which
case the system chooses a protocol type to use, based on the socket type.
Sockets of type SOCK_STREAM are byte streams similar to UNIX pipes,
except that they are full-duplex instead of half-duplex. A stream socket must
be in a connected state before any data can be sent or received on it. A
connection to another socket is created with a connect or
accept call. Once connected, data can be transferred using
send and recv calls or read and write
calls. When a session has been completed, a close can be performed.
The communications protocol (TCP) used to implement
SOCK_STREAM for AF_INET sockets, ensures that data is not
lost or duplicated. If a peer has buffer space for data and the data cannot be
successfully transmitted within a reasonable length of time, the connection is
considered broken and the next recv call indicates an error with
errno set to ETIMEDOUT. An end-of-file condition
(zero bytes read) is returned if a process tries to read on a broken stream.
To use the errno global variable, include the file
<sys/errno.h>.
SOCK_DGRAM sockets allow sending of messages to correspondents named
in sendto calls. It is also possible to receive messages at a
SOCK_DGRAM socket with recvfrom. The sockets operation is
controlled by socket level options set by the setsockopt system call.
(Refer to getsockopt or
setsockopt.) These options are defined in the file
<sys/socket.h>.
Return Value
If the call is successful, a valid file descriptor referencing the socket is
returned. If it fails, a -1 is returned, and an error code is stored in
errno.
Errors
The following errors are returned by socket:
| Error Code |
Description |
| [EHOSTDOWN] |
The networking subsystem has not been started. |
| [EAFNOSUPPORT] |
The specified address family is not supported on this version of the
system. |
| [ESOCKTNOSUPPORT] |
The specified socket type is not supported in this address family. |
| [EPROTONOSUPPORT] |
The specified protocol is not supported. |
| [EMFILE] |
The per-process descriptor table is full. |
| [ENOBUFS] |
No buffer space is available. The socket cannot be created. |
| [ENFILE] |
The system's table of open files is temporarily full, and no more
socket calls can be accepted. |
| [EPROTOTYPE] |
The type of socket and protocol do not match. |
| [ETIMEDOUT] |
The connection timed out. |
MPE/iX Specific
Break mode is supported on MPE/iX. This is true of all Berkeley Sockets/iX
system calls described in this section.
Author
UCB (University of California at Berkeley)
See Also
getsockopt,
setsockopt
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