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
12 sendto — send a message on a socket
13
15 #include <sys/socket.h>
16 ssize_t sendto(int socket, const void *message, size_t length,
18 int flags, const struct sockaddr *dest_addr,
19 socklen_t dest_len);
20
22 The sendto() function shall send a message through a connection-mode or
23 connectionless-mode socket.
24 If the socket is a connectionless-mode socket, the message shall be
26 sent to the address specified by dest_addr if no pre-specified peer
27 address has been set. If a peer address has been pre-specified, either
28 the message shall be sent to the address specified by dest_addr (over‐
29 riding the pre-specified peer address), or the function shall return -1
30 and set errno to [EISCONN].
31 If the socket is connection-mode, dest_addr shall be ignored.
33 The sendto() function takes the following arguments:
35 socket Specifies the socket file descriptor.
37 message Points to a buffer containing the message to be sent.
39 length Specifies the size of the message in bytes.
41 flags Specifies the type of message transmission. Values of this
43 argument are formed by logically OR'ing zero or more of the
44 following flags:
45 MSG_EOR Terminates a record (if supported by the pro‐
47 tocol).
48 MSG_OOB Sends out-of-band data on sockets that sup‐
50 port out-of-band data. The significance and
51 semantics of out-of-band data are protocol-
52 specific.
53 MSG_NOSIGNAL Requests not to send the SIGPIPE signal if an
55 attempt to send is made on a stream-oriented
56 socket that is no longer connected. The
57 [EPIPE] error shall still be returned.
58 dest_addr Points to a sockaddr structure containing the destination
60 address. The length and format of the address depend on the
61 address family of the socket.
62 dest_len Specifies the length of the sockaddr structure pointed to
64 by the dest_addr argument.
65 If the socket protocol supports broadcast and the specified address is
67 a broadcast address for the socket protocol, sendto() shall fail if the
68 SO_BROADCAST option is not set for the socket.
69 The dest_addr argument specifies the address of the target.
71 The length argument specifies the length of the message.
73 Successful completion of a call to sendto() does not guarantee delivery
75 of the message. A return value of -1 indicates only locally-detected
76 errors.
77 If space is not available at the sending socket to hold the message to
79 be transmitted and the socket file descriptor does not have O_NONBLOCK
80 set, sendto() shall block until space is available. If space is not
81 available at the sending socket to hold the message to be transmitted
82 and the socket file descriptor does have O_NONBLOCK set, sendto() shall
83 fail.
84 The socket in use may require the process to have appropriate privi‐
86 leges to use the sendto() function.
87
89 Upon successful completion, sendto() shall return the number of bytes
90 sent. Otherwise, -1 shall be returned and errno set to indicate the
91 error.
92
94 The sendto() function shall fail if:
95 EAFNOSUPPORT
97 Addresses in the specified address family cannot be used with
98 this socket.
99 EAGAIN or EWOULDBLOCK
101 The socket's file descriptor is marked O_NONBLOCK and the
102 requested operation would block.
103 EBADF The socket argument is not a valid file descriptor.
105 ECONNRESET
107 A connection was forcibly closed by a peer.
108 EINTR A signal interrupted sendto() before any data was transmitted.
110 EMSGSIZE
112 The message is too large to be sent all at once, as the socket
113 requires.
114 ENOTCONN
116 The socket is connection-mode but is not connected.
117 ENOTSOCK
119 The socket argument does not refer to a socket.
120 EOPNOTSUPP
122 The socket argument is associated with a socket that does not
123 support one or more of the values set in flags.
124 EPIPE The socket is shut down for writing, or the socket is connec‐
126 tion-mode and is no longer connected. In the latter case, and if
127 the socket is of type SOCK_STREAM or SOCK_SEQPACKET and the
128 MSG_NOSIGNAL flag is not set, the SIGPIPE signal is generated to
129 the calling thread.
130 If the address family of the socket is AF_UNIX, then sendto() shall
132 fail if:
133 EIO An I/O error occurred while reading from or writing to the file
135 system.
136 ELOOP A loop exists in symbolic links encountered during resolution of
138 the pathname in the socket address.
139 ENAMETOOLONG
141 The length of a component of a pathname is longer than
142 {NAME_MAX}.
143 ENOENT A component of the pathname does not name an existing file or
145 the pathname is an empty string.
146 ENOTDIR
148 A component of the path prefix of the pathname in the socket
149 address names an existing file that is neither a directory nor a
150 symbolic link to a directory, or the pathname in the socket
151 address contains at least one non-<slash> character and ends
152 with one or more trailing <slash> characters and the last path‐
153 name component names an existing file that is neither a direc‐
154 tory nor a symbolic link to a directory.
155 The sendto() function may fail if:
157 EACCES Search permission is denied for a component of the path prefix;
159 or write access to the named socket is denied.
160 EDESTADDRREQ
162 The socket is not connection-mode and does not have its peer
163 address set, and no destination address was specified.
164 EHOSTUNREACH
166 The destination host cannot be reached (probably because the
167 host is down or a remote router cannot reach it).
168 EINVAL The dest_len argument is not a valid length for the address fam‐
170 ily.
171 EIO An I/O error occurred while reading from or writing to the file
173 system.
174 EISCONN
176 A destination address was specified and the socket is already
177 connected.
178 ENETDOWN
180 The local network interface used to reach the destination is
181 down.
182 ENETUNREACH
184 No route to the network is present.
185 ENOBUFS
187 Insufficient resources were available in the system to perform
188 the operation.
189 ENOMEM Insufficient memory was available to fulfill the request.
191 If the address family of the socket is AF_UNIX, then sendto() may fail
193 if:
194 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
196 resolution of the pathname in the socket address.
197 ENAMETOOLONG
199 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
200 tion of a symbolic link produced an intermediate result with a
201 length that exceeds {PATH_MAX}.
202 The following sections are informative.
204
206 None.
207
209 The select() and poll() functions can be used to determine when it is
210 possible to send more data.
211
213 None.
214
216 None.
217
219 getsockopt(), poll(), pselect(), recv(), recvfrom(), recvmsg(), send(),
220 sendmsg(), setsockopt(), shutdown(), socket()
221 The Base Definitions volume of POSIX.1‐2017, <sys_socket.h>
223
225 Portions of this text are reprinted and reproduced in electronic form
226 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
227 table Operating System Interface (POSIX), The Open Group Base Specifi‐
228 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
229 Electrical and Electronics Engineers, Inc and The Open Group. In the
230 event of any discrepancy between this version and the original IEEE and
231 The Open Group Standard, the original IEEE and The Open Group Standard
232 is the referee document. The original Standard can be obtained online
233 at http://www.opengroup.org/unix/online.html .
234 Any typographical or formatting errors that appear in this page are
236 most likely to have been introduced during the conversion of the source
237 files to man page format. To report such errors, see https://www.ker‐
238 nel.org/doc/man-pages/reporting_bugs.html .
239IEEE/The Open Group 2017 SENDTO(3P)