send a message from a socket
cc [options] file -lsocket -lnsl
ssize_t send(int s, const void *msg, size_t len, int flags);
ssize_t sendto(int s, const void *msg, size_t len, int flags,
const struct sockaddr *to, size_t tolen);
ssize_t sendmsg(int s, const struct msghdr *msg, int flags);
s is a socket created with socket.
send, sendto, and sendmsg
are used to transmit a message to another socket.
send may be used only when the socket is in a
state, while sendto and sendmsg
may be used at any time.
The address of the target is given by
specifying its size.
The length of the message is given by
If the message is too long to pass automatically through the
underlying protocol, then the error
is returned, and the message is not transmitted.
No indication of failure to deliver is implicit in a send.
Return values of -1 indicate some locally detected errors.
If no buffer space is available at the socket to hold
the message to be transmitted, then send
normally blocks, unless the socket has been placed in
non-blocking I/O mode (O_NONBLOCK).
The select call may be used to determine when it is
possible to send more data.
If the socket protocol supports broadcasting and the specified address
is a broadcast address, sendto and sendmsg will fail if
the SO_BROADCAST option is not set for the socket.
The flags parameter is formed by ORing
one or more of the following:
Requests not to send SIGPIPE on errors on stream oriented sockets
when the other end breaks the connection. The EPIPE error is
data on sockets that support this notion.
The underlying protocol must also
support out-of-band data.
Currently, only SOCK_STREAM
sockets created in the
AF_INET and AF_INET6
address families support out-of-band data.
option is turned on for the duration of the operation.
It is used only by diagnostic or routing programs.
Enables non-blocking operation; if the operation would block,
EAGAIN is returned.
for a description of the
These calls return the number of bytes sent,
or -1 if an error occurred.
The calls fail if:
No search permission for a component of the specified path, or
no write permission on a named socket (AF_UNIX only).
The specified address family cannot be used with the socket.
s is an invalid descriptor.
The peer forcibly closed the connection.
The socket is not connection-oriented and a peer address is not set.
The operation was interrupted by delivery of a signal before
any data could be buffered to be sent.
tolen is not the size of a
valid address for the specified address family.
An I/O error occurred while writing to or reading from the filesystem
Too many symbolic links when translating the pathname in the socket
address (AF_UNIX only).
A component of the pathname or the entire pathname was too long
The socket requires that message be sent atomically,
and the message was too long.
A component of the pathname or the entire pathname does not refer to an
existing file (AF_UNIX only).
There was insufficient user memory available for the operation to complete.
s is a descriptor for a file, not a socket.
The socket is not connected or the peer has not been prespecified.
A component of the pathname is not a directory
The socket does not support a value set in flags.
The socket is connection-oriented and
the peer is closed or shut down for reading
(generates SIGPIPE to calling
process if type is SOCK_STREAM),
or the socket is shut down for writing.
There were insufficient STREAMS
resources available for the operation to complete.
The socket is marked non-blocking and the requested operation would block.
The type of address structure passed to sendto and
sendmsg depends on the address family.
UNIX® domain sockets (address family AF_UNIX) require a
sockaddr_un structure as defined in sys/un.h;
Internet domain IPv4 sockets (address family AF_INET)
require a struct sockaddr_in structure as defined in
Internet domain IPv6 sockets (address family AF_INET6)
require a struct sockaddr_in6 structure as defined in
Other address families may require other structures.
Use the structure appropriate to the address family; cast the
structure address to a struct sockaddr* in the call to
and pass the size of the structure in the fromlen argument. If
you are using sendmsg, set
msghdr.msg_name to point
to the appropriate structure and
msghdr.msg_namelen to the
length of the structure.
In UnixWare 7 the sockaddr structure has been modified
to support variable length sockets. The net result of this modification
is that the
family member has been shortened to 8 bits and a
new 8-bit member inserted before it called
len. For more
information on the new sockaddr structures, see:
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004