1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)send.2 8.2 (Berkeley) 02/21/94 7.\" 8.Dd 9.Dt SEND 2 10.Os BSD 4.2 11.Sh NAME 12.Nm send , 13.Nm sendto , 14.Nm sendmsg 15.Nd send a message from a socket 16.Sh SYNOPSIS 17.Fd #include <sys/types.h> 18.Fd #include <sys/socket.h> 19.Ft ssize_t 20.Fn send "int s" "const void *msg" "size_t len" "int flags" 21.Ft ssize_t 22.Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "int tolen" 23.Ft ssize_t 24.Fn sendmsg "int s" "const struct msghdr *msg" "int flags" 25.Sh DESCRIPTION 26.Fn Send , 27.Fn sendto , 28and 29.Fn sendmsg 30are used to transmit a message to another socket. 31.Fn Send 32may be used only when the socket is in a 33.Em connected 34state, while 35.Fn sendto 36and 37.Fn sendmsg 38may be used at any time. 39.Pp 40The address of the target is given by 41.Fa to 42with 43.Fa tolen 44specifying its size. 45The length of the message is given by 46.Fa len . 47If the message is too long to pass atomically through the 48underlying protocol, the error 49.Er EMSGSIZE 50is returned, and 51the message is not transmitted. 52.Pp 53No indication of failure to deliver is implicit in a 54.Fn send . 55Locally detected errors are indicated by a return value of -1. 56.Pp 57If no messages space is available at the socket to hold 58the message to be transmitted, then 59.Fn send 60normally blocks, unless the socket has been placed in 61non-blocking I/O mode. 62The 63.Xr select 2 64call may be used to determine when it is possible to 65send more data. 66.Pp 67The 68.Fa flags 69parameter may include one or more of the following: 70.Bd -literal 71#define MSG_OOB 0x1 /* process out-of-band data */ 72#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ 73.Ed 74.Pp 75The flag 76.Dv MSG_OOB 77is used to send 78.Dq out-of-band 79data on sockets that support this notion (e.g. 80.Dv SOCK_STREAM ) ; 81the underlying protocol must also support 82.Dq out-of-band 83data. 84.Dv MSG_DONTROUTE 85is usually used only by diagnostic or routing programs. 86.Pp 87See 88.Xr recv 2 89for a description of the 90.Fa msghdr 91structure. 92.Sh RETURN VALUES 93The call returns the number of characters sent, or -1 94if an error occurred. 95.Sh ERRORS 96.Fn Send , 97.Fn sendto , 98and 99.Fn sendmsg 100fail if: 101.Bl -tag -width [EMSGSIZE] 102.It Bq Er EBADF 103An invalid descriptor was specified. 104.It Bq Er ENOTSOCK 105The argument 106.Fa s 107is not a socket. 108.It Bq Er EFAULT 109An invalid user space address was specified for a parameter. 110.It Bq Er EMSGSIZE 111The socket requires that message be sent atomically, 112and the size of the message to be sent made this impossible. 113.It Bq Er EAGAIN 114The socket is marked non-blocking and the requested operation 115would block. 116.It Bq Er ENOBUFS 117The system was unable to allocate an internal buffer. 118The operation may succeed when buffers become available. 119.It Bq Er ENOBUFS 120The output queue for a network interface was full. 121This generally indicates that the interface has stopped sending, 122but may be caused by transient congestion. 123.El 124.Sh SEE ALSO 125.Xr fcntl 2 , 126.Xr recv 2 , 127.Xr select 2 , 128.Xr getsockopt 2 , 129.Xr socket 2 , 130.Xr write 2 131.Sh HISTORY 132The 133.Nm 134function call appeared in 135.Bx 4.2 . 136