send, sendto, sendmsg - send a message from a socket
int send(int s, char *msg, int len, int flags);
int sendto(int s, char *msg, int len, int flags, caddr_t to,
int sendmsg(int s, 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 connected state, while sendto and sendmsg may be used at
The address of the target is given by to with tolen specifying its size.
The length of the message is given by len. If the message is too long to
pass atomically through the underlying protocol, then the error EMSGSIZE
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 [see fcntl(2)]. The select call may be used to
determine when it is possible to send more data.
The flags parameter is formed by ORing one or more of the following:
MSG_OOB Send out-of-band 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
address family support out-of-band data.
The SO_DONTROUTE option is turned on for the duration of the
operation. It is used only by diagnostic or routing programs.
See recv(3N) for a description of the msghdr structure.
These calls return the number of bytes sent, or -1 if an error occurred.
The calls fail if:
EBADF s is an invalid descriptor.
ENOTSOCK s is a descriptor for a file, not a socket.
EINVAL tolen is not the size of a valid address for the
specified address family.
EINTR The operation was interrupted by delivery of a signal
before any data could be buffered to be sent.
EMSGSIZE The socket requires that message be sent atomically,
and the message was too long.
EWOULDBLOCK The socket is marked non-blocking and the requested
operation would block.
ENOMEM There was insufficient user memory available for the
operation to complete.
ENOSR There were insufficient STREAMS resources available
for the operation to complete.
fcntl(2), write(2), connect(3N), getsockopt(3N), recv(3N), socket(3N)
The type of address structure passed to accept depends on the address
family. UNIX domain sockets (address family AF_UNIX) require a
socketaddr_un structure as defined in sys/un.h; Internet domain sockets
(address family AF_INET) require a sockaddr_in structure as defined in
netinet/in.h. Other address families may require other structures. Use
the structure appropriate to the address family; cast the structure
address to a generic caddr_t in the call to send and pass the size of the
structure in the tolen argument.
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