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NAMEsend, sendto, sendmsg - send a message from a socket
ssize_t send(int s, const void *buf, size_t len,
DESCRIPTIONThe system calls send, sendto, and sendmsg are used to transmit a message to another socket.
The send call may be used only when the socket is in a connected state (so that the intended recipient is known). The only difference between send and write is the presence of flags. With zero flags parameter, send is equivalent to write. Also, send(s,buf,len) is equivalent to sendto(s,buf,len,NULL,0).
The parameter s is the file descriptor of the sending socket.
If sendto is used on a connection-mode (SOCK_STREAM, SOCK_SEQPACKET) socket, the parameters to and tolen are ignored (and the error EISCONN may be returned when they are not NULL and 0), and the error ENOTCONN is returned when the socket was not actually connected. Otherwise, the address of the target is given by to with tolen specifying its size. For sendmsg, the address of the target is given by msg.msg_name, with msg.msg_namelen specifying its size.
For send and sendto, the message is found in buf and has length len. For sendmsg, the message is pointed to by the elements of the array msg.msg_iov. The sendmsg call also allows sending ancillary data (also known as control information).
If the message is too long to pass atomically through the underlying protocol, the error EMSGSIZE is returned, and the message is not transmitted.
No indication of failure to deliver is implicit in a send. Locally detected errors are indicated by a return value of -1.
When the message does not fit into the send buffer of the socket, send normally blocks, unless the socket has been placed in non-blocking I/O mode. In non-blocking mode it would return EAGAIN in this case. The select(2) call may be used to determine when it is possible to send more data.
The flags parameter is the bitwise OR of zero or more of the following flags.
The definition of the msghdr structure follows. See recv(2) and below for an exact description of its fields.
You may send control information using the msg_control and msg_controllen members. The maximum control buffer length the kernel can process is limited per socket by the net.core.optmem_max sysctl; see socket(7).
RETURN VALUEThe calls return the number of characters sent, or -1 if an error occurred.
ERRORSThese are some standard errors generated by the socket layer. Additional errors may be generated and returned from the underlying protocol modules; see their respective manual pages.
CONFORMING TO4.4BSD, SVr4, POSIX 1003.1-2001. These function calls appeared in 4.2BSD.
NOTEThe prototypes given above follow the Single Unix Specification, as glibc2 also does; the flags argument was `int' in BSD 4.*, but `unsigned int' in libc4 and libc5; the len argument was `int' in BSD 4.* and libc4, but `size_t' in libc5; the tolen argument was `int' in BSD 4.* and libc4 and libc5. See also accept(2).
BUGSLinux may return EPIPE instead of ENOTCONN.
SEE ALSOfcntl(2), recv(2), select(2), getsockopt(2), sendfile(2), socket(2), write(2), socket(7), ip(7), tcp(7), udp(7)