1SENDTO(3P) POSIX Programmer's Manual SENDTO(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 sendto — send a message on a socket
14
16 #include <sys/socket.h>
17 ssize_t sendto(int socket, const void *message, size_t length,
19 int flags, const struct sockaddr *dest_addr,
20 socklen_t dest_len);
21
23 The sendto() function shall send a message through a connection-mode or
24 connectionless-mode socket.
25 If the socket is a connectionless-mode socket, the message shall be
27 sent to the address specified by dest_addr if no pre-specified peer
28 address has been set. If a peer address has been pre-specified, either
29 the message shall be sent to the address specified by dest_addr (over‐
30 riding the pre-specified peer address), or the function shall return −1
31 and set errno to [EISCONN].
32 If the socket is connection-mode, dest_addr shall be ignored.
34 The sendto() function takes the following arguments:
36 socket Specifies the socket file descriptor.
38 message Points to a buffer containing the message to be sent.
40 length Specifies the size of the message in bytes.
42 flags Specifies the type of message transmission. Values of this
44 argument are formed by logically OR'ing zero or more of the
45 following flags:
46 MSG_EOR Terminates a record (if supported by the pro‐
48 tocol).
49 MSG_OOB Sends out-of-band data on sockets that sup‐
51 port out-of-band data. The significance and
52 semantics of out-of-band data are protocol-
53 specific.
54 MSG_NOSIGNAL Requests not to send the SIGPIPE signal if an
56 attempt to send is made on a stream-oriented
57 socket that is no longer connected. The
58 [EPIPE] error shall still be returned.
59 dest_addr Points to a sockaddr structure containing the destination
61 address. The length and format of the address depend on the
62 address family of the socket.
63 dest_len Specifies the length of the sockaddr structure pointed to
65 by the dest_addr argument.
66 If the socket protocol supports broadcast and the specified address is
68 a broadcast address for the socket protocol, sendto() shall fail if the
69 SO_BROADCAST option is not set for the socket.
70 The dest_addr argument specifies the address of the target.
72 The length argument specifies the length of the message.
74 Successful completion of a call to sendto() does not guarantee delivery
76 of the message. A return value of −1 indicates only locally-detected
77 errors.
78 If space is not available at the sending socket to hold the message to
80 be transmitted and the socket file descriptor does not have O_NONBLOCK
81 set, sendto() shall block until space is available. If space is not
82 available at the sending socket to hold the message to be transmitted
83 and the socket file descriptor does have O_NONBLOCK set, sendto() shall
84 fail.
85 The socket in use may require the process to have appropriate privi‐
87 leges to use the sendto() function.
88
90 Upon successful completion, sendto() shall return the number of bytes
91 sent. Otherwise, −1 shall be returned and errno set to indicate the
92 error.
93
95 The sendto() function shall fail if:
96 EAFNOSUPPORT
98 Addresses in the specified address family cannot be used with
99 this socket.
100 EAGAIN or EWOULDBLOCK
102 The socket's file descriptor is marked O_NONBLOCK and the
103 requested operation would block.
104 EBADF The socket argument is not a valid file descriptor.
106 ECONNRESET
108 A connection was forcibly closed by a peer.
109 EINTR A signal interrupted sendto() before any data was transmitted.
111 EMSGSIZE
113 The message is too large to be sent all at once, as the socket
114 requires.
115 ENOTCONN
117 The socket is connection-mode but is not connected.
118 ENOTSOCK
120 The socket argument does not refer to a socket.
121 EOPNOTSUPP
123 The socket argument is associated with a socket that does not
124 support one or more of the values set in flags.
125 EPIPE The socket is shut down for writing, or the socket is connec‐
127 tion-mode and is no longer connected. In the latter case, and if
128 the socket is of type SOCK_STREAM or SOCK_SEQPACKET and the
129 MSG_NOSIGNAL flag is not set, the SIGPIPE signal is generated to
130 the calling thread.
131 If the address family of the socket is AF_UNIX, then sendto() shall
133 fail if:
134 EIO An I/O error occurred while reading from or writing to the file
136 system.
137 ELOOP A loop exists in symbolic links encountered during resolution of
139 the pathname in the socket address.
140 ENAMETOOLONG
142 The length of a component of a pathname is longer than
143 {NAME_MAX}.
144 ENOENT A component of the pathname does not name an existing file or
146 the pathname is an empty string.
147 ENOTDIR
149 A component of the path prefix of the pathname in the socket
150 address names an existing file that is neither a directory nor a
151 symbolic link to a directory, or the pathname in the socket
152 address contains at least one non-<slash> character and ends
153 with one or more trailing <slash> characters and the last path‐
154 name component names an existing file that is neither a direc‐
155 tory nor a symbolic link to a directory.
156 The sendto() function may fail if:
158 EACCES Search permission is denied for a component of the path prefix;
160 or write access to the named socket is denied.
161 EDESTADDRREQ
163 The socket is not connection-mode and does not have its peer
164 address set, and no destination address was specified.
165 EHOSTUNREACH
167 The destination host cannot be reached (probably because the
168 host is down or a remote router cannot reach it).
169 EINVAL The dest_len argument is not a valid length for the address fam‐
171 ily.
172 EIO An I/O error occurred while reading from or writing to the file
174 system.
175 EISCONN
177 A destination address was specified and the socket is already
178 connected.
179 ENETDOWN
181 The local network interface used to reach the destination is
182 down.
183 ENETUNREACH
185 No route to the network is present.
186 ENOBUFS
188 Insufficient resources were available in the system to perform
189 the operation.
190 ENOMEM Insufficient memory was available to fulfill the request.
192 If the address family of the socket is AF_UNIX, then sendto() may fail
194 if:
195 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
197 resolution of the pathname in the socket address.
198 ENAMETOOLONG
200 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
201 tion of a symbolic link produced an intermediate result with a
202 length that exceeds {PATH_MAX}.
203 The following sections are informative.
205
207 None.
208
210 The select() and poll() functions can be used to determine when it is
211 possible to send more data.
212
214 None.
215
217 None.
218
220 getsockopt(), poll(), pselect(), recv(), recvfrom(), recvmsg(), send(),
221 sendmsg(), setsockopt(), shutdown(), socket()
222 The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>
224
226 Portions of this text are reprinted and reproduced in electronic form
227 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
228 -- Portable Operating System Interface (POSIX), The Open Group Base
229 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
230 cal and Electronics Engineers, Inc and The Open Group. (This is
231 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
232 event of any discrepancy between this version and the original IEEE and
233 The Open Group Standard, the original IEEE and The Open Group Standard
234 is the referee document. The original Standard can be obtained online
235 at http://www.unix.org/online.html .
236 Any typographical or formatting errors that appear in this page are
238 most likely to have been introduced during the conversion of the source
239 files to man page format. To report such errors, see https://www.ker‐
240 nel.org/doc/man-pages/reporting_bugs.html .
241IEEE/The Open Group 2013 SENDTO(3P)