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@(#)send.2 8.2 (Berkeley) 2/21/94
.Dd February 21, 1994 .Dt SEND 2 .Os BSD 4.2 .Sh NAME .Nm send , .Nm sendto , .Nm sendmsg .Nd send a message from a socket .Sh SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/socket.h> .Ft ssize_t .Fn send "int s" "const void *msg" "size_t len" "int flags" .Ft ssize_t .Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "int tolen" .Ft ssize_t .Fn sendmsg "int s" "const struct msghdr *msg" "int flags" .Sh DESCRIPTION .Fn Send , .Fn sendto , and .Fn sendmsg are used to transmit a message to another socket. .Fn Send may be used only when the socket is in a .Em connected state, while .Fn sendto and .Fn sendmsg may be used at any time.
p The address of the target is given by .Fa to with .Fa tolen specifying its size. The length of the message is given by .Fa len . If the message is too long to pass atomically through the underlying protocol, the error .Er EMSGSIZE is returned, and the message is not transmitted.
p No indication of failure to deliver is implicit in a .Fn send . Locally detected errors are indicated by a return value of -1.
p If no messages space is available at the socket to hold the message to be transmitted, then .Fn send normally blocks, unless the socket has been placed in non-blocking I/O mode. The .Xr select 2 call may be used to determine when it is possible to send more data.
p The .Fa flags parameter may include one or more of the following: d -literal #define MSG_OOB 0x1 /* process out-of-band data */ #define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ .Ed
p The flag .Dv MSG_OOB is used to send .Dq out-of-band data on sockets that support this notion (e.g. .Dv SOCK_STREAM ) ; the underlying protocol must also support .Dq out-of-band data. .Dv MSG_DONTROUTE is usually used only by diagnostic or routing programs.
p See .Xr recv 2 for a description of the .Fa msghdr structure. .Sh RETURN VALUES The call returns the number of characters sent, or -1 if an error occurred. .Sh ERRORS .Fn Send , .Fn sendto , and .Fn sendmsg fail if: l -tag -width [EMSGSIZE] t Bq Er EBADF An invalid descriptor was specified. t Bq Er ENOTSOCK The argument .Fa s is not a socket. t Bq Er EFAULT An invalid user space address was specified for a parameter. t Bq Er EMSGSIZE The socket requires that message be sent atomically, and the size of the message to be sent made this impossible. t Bq Er EAGAIN The socket is marked non-blocking and the requested operation would block. t Bq Er ENOBUFS The system was unable to allocate an internal buffer. The operation may succeed when buffers become available. t Bq Er ENOBUFS The output queue for a network interface was full. This generally indicates that the interface has stopped sending, but may be caused by transient congestion. .El .Sh SEE ALSO .Xr fcntl 2 , .Xr recv 2 , .Xr select 2 , .Xr getsockopt 2 , .Xr socket 2 , .Xr write 2 .Sh HISTORY The .Nm function call appeared in x 4.2 .