bind — bind a name to a socket
#include <sys/types.h> /* See NOTES */ #include <sys/socket.h>
int
bind( |
int | sockfd, |
const struct sockaddr * | my_addr, | |
socklen_t | addrlen) ; |
bind
() gives the socket
sockfd
the local
address my_addr
.
my_addr
is addrlen
bytes long.
Traditionally, this is called “assigning a name to a socket”. When a
socket is created with socket(2), it exists in a
name space (address family) but has no name assigned.
It is normally necessary to assign a local address using
bind
() before a SOCK_STREAM
socket may receive connections
(see accept(2)).
The rules used in name binding vary between address
families. Consult the manual entries in Section 7 for
detailed information. For AF_INET
see ip(7), for AF_INET6
see ipv6(7), for AF_UNIX
see unix(7), for AF_APPLETALK
see ddp(7), for AF_PACKET
see packet(7), for AF_X25
see x25(7) and for AF_NETLINK
see netlink(7).
The actual structure passed for the my_addr
argument will depend on
the address family. The sockaddr
structure is defined
as something like:
struct sockaddr { sa_family_t sa_family
;char sa_data
[14];};
The only purpose of this structure is to cast the
structure pointer passed in my_addr
in order to avoid
compiler warnings. See EXAMPLE below.
On success, zero is returned. On error, −1 is
returned, and errno
is set
appropriately.
The address is protected, and the user is not the superuser.
The given address is already in use.
sockfd
is
not a valid descriptor.
The socket is already bound to an address.
sockfd
is a
descriptor for a file, not a socket.
The following errors are specific to UNIX domain
(AF_UNIX
) sockets:
Search permission is denied on a component of the path prefix. (See also path_resolution(7).)
A non-existent interface was requested or the requested address was not local.
my_addr
points outside the user's accessible address space.
The addrlen
is wrong, or the socket was not in the AF_UNIX
family.
Too many symbolic links were encountered in
resolving my_addr
.
my_addr
is
too long.
The file does not exist.
Insufficient kernel memory was available.
A component of the path prefix is not a directory.
The socket inode would reside on a read-only file system.
POSIX.1-2001 does not require the inclusion of <sys/types.h>
, and this
header file is not required on Linux. However, some
historical (BSD) implementations required this header file,
and portable applications are probably wise to include
it.
The third argument of bind
()
is in reality an int
(and this is what 4.x BSD
and libc4 and libc5 have). Some POSIX confusion resulted in
the present socklen_t
, also used by
glibc. See also accept(2).
An example of the use of bind
() with Internet domain sockets can be
found in getaddrinfo(3).
The following example shows how to bind a stream socket in
the Unix (AF_UNIX
) domain, and
accept connections:
#include <sys/socket.h> #include <sys/un.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #define MY_SOCK_PATH "/somepath" #define LISTEN_BACKLOG 50 #define die(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0) int main(int argc, char *argv[]) { int sfd, cfd; struct sockaddr_un my_addr, peer_addr; socklen_t peer_addr_size; sfd = socket(AF_UNIX, SOCK_STREAM, 0); if (sfd == −1) die("socket"); memset(&my_addr, 0, sizeof(struct sockaddr_un)); /* Clear structure */ my_addr.sun_family = AF_UNIX; strncpy(my_addr.sun_path, MY_SOCK_PATH, sizeof(my_addr.sun_path) − 1); if (bind(sfd, (struct sockaddr *) &my_addr, sizeof(struct sockaddr_un)) == −1) die("bind"); if (listen(sfd, LISTEN_BACKLOG) == −1) die("listen"); /* Now we can accept incoming connections one at a time using accept(2) */ peer_addr_size = sizeof(struct sockaddr_un); cfd = accept(sfd, (struct sockaddr *) &peer_addr, &peer_addr_size) if (cfd == −1) die("accept"); /* Code to deal with incoming connection(s)... */ /* When no longer required, the socket pathname, MY_SOCK_PATH should be deleted using unlink(2) or remove(3) */ }
accept(2), connect(2), getsockname(2), listen(2), socket(2), getaddrinfo(3), ip(7), ipv6(7), path_resolution(7), socket(7), unix(7)
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