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sendto(2)
NAME
sendto - Send messages through a socket
SYNOPSIS
#include <sys/socket.h>
ssize_t sendto(
int socket,
const void *message,
size_t length,
int flags,
const struct sockaddr *dest_addr,
socklen_t dest_len );
[XNS4.0] The definition of the sendto() function in XNS4.0 uses a size_t
data type for the dest_len parameter instead of a socklen_t data type as
specified in XNS5.0 (the previous definition).
[Tru64 UNIX] The following definition of the sendto() function does not
conform to current standards and is supported only for backward
compatibility (see standards(5)):
#include <sys/socket.h>
int sendto(
int socket,
char *message_addr,
int length,
int flags,
struct sockaddr *dest_addr,
int dest_len );
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
sendto(): XNS4.0, XNS5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
socket
Specifies the file descriptor for the socket.
message
Points to the address containing the message to be sent.
length
Specifies the size of the message in bytes.
flags
Allows the sender to control the message transmission. The flags value
to send a call is formed by logically ORing the following values,
defined in the sys/socket.h file:
MSG_EOR
Terminates a record (if supported by the protocol).
MSG_OOB
Processes out-of-band data on sockets that support out-of-band
data.
MSG_DONTROUTE
[Tru64 UNIX] Sends without using routing tables. (Not recommended;
for debugging purposes only.)
dest_addr
Points to a sockaddr structure, the format of which is determined by
the domain and by the behavior requested for the socket. The sockaddr
structure is an overlay for a sockaddr_in, sockaddr_un, sockaddr_in6,
or sockaddr_storage structure, depending on which of the supported
address families is active.
[Tru64 UNIX] If the compile-time option _SOCKADDR_LEN is defined
before the sys/socket.h header file is included, the sockaddr structure
takes 4.4BSD behavior, with a field for specifying the length of the
socket address. Otherwise, the default 4.3BSD sockaddr structure is
used, with the length of the socket address assumed to be 14 bytes or
less.
If _SOCKADDR_LEN is defined, the 4.3BSD sockaddr structure is defined
with the name osockaddr.
dest_len
Specifies the length of the sockaddr structure pointed to by the
dest_addr parameter.
DESCRIPTION
The sendto() function allows an application program to send messages
through an unconnected socket by specifying a destination address.
To broadcast on a socket, issue a setsockopt() function using the
SO_BROADCAST option to gain broadcast permissions.
Use the dest_addr parameter to provide the address of the target. Specify
the length of the message with the length parameter.
If the sending socket has no space to hold the message to be transmitted,
the sendto() function blocks unless the socket is in a nonblocking I/O
mode.
Use the select() and poll() functions to determine when to send more data.
RETURN VALUES
Upon successful completion, the sendto() function returns the number of
characters sent. Otherwise, a value of -1 is returned, anderrno is set to
indicate the error.
ERRORS
If the sendto() function fails, errno may be set to one of the following
values:
[EACCESS]
Search permission is denied for a component of the path prefix; or
write access to the named socket is denied.
[EAFNOSUPPORT]
Addresses in the specified address family cannot be used with this
socket.
[EBADF]
The socket parameter is not valid.
[ECONNRESET]
A connection was forcibly closed by a peer.
[EDESTADDRREQ]
You did not specify a destination address for the connectionless socket
that also did not have its peer address set.
[EFAULT]
The message or dest_addr parameter is not in a writable part of the
user address space.
[EHOSTUNREACH]
The destination host is not reachable.
[EINTR]
A signal interrupted sendto before any data was transmitted.
[EINVAL]
The dest_len parameter is not a valid size for the specified address
family.
[EIO]
For an AF_UNIX socket, an I/O error occurred while reading from or
writing to the file system.
[EISCONN]
The connection-oriented socket for which a destination address was
specified is already connected.
[ELOOP]
For an AF_UNIX socket, too many symbolic links were encountered in
translating the pathname in the socket address.
[EMSGSIZE]
The message is too large to be sent all at once, as the socket
requires.
[ENAMETOOLONG]
For an AF_UNIX socket, a component of the pathname exceeded NAME_MAX
characters, or an entire pathname exceeded PATH_MAX characters.
[ENETDOWN]
The local network connection is not operational.
[ENETUNREACH]
The destination network is unreachable.
[ENOBUFS]
Insufficient resources are available in the system to complete the
call.
[Tru64 UNIX] The interface driver's send queue is full. If the problem
persists, you might increase the value for the ifqmaxlen system
attribute in the net subsystem. See sys_attrs_net(5) for more
information.
[ENOENT]
For an AF_UNIX socket, a component of the pathname does not name an
existing file or the pathname is an empty string.
[ENOMEM]
The system did not have sufficient memory to fulfill the request.
[ENOSR]
The available STREAMS resources were insufficient for the operation to
complete.
[ENOTCONN]
The socket is connection-oriented but is not connected.
[ENOTDIR]
For an AF_UNIX socket, a component of the path prefix of the pathname
in address is not a directory.
[ENOTSOCK]
The socket parameter refers to a file, not a socket.
[EOPNOTSUPP]
The socket argument is associated with a socket that does not support
one or more of the values set in flags.
[EPIPE]
The socket is shut down for writing, or the socket is connection-
oriented and the peer is closed or shut down for reading. In the latter
case, and if the socket is of type SOCK_STREAM, the SIGPIPE signal is
generated to the calling process.
[EWOULDBLOCK]
The socket is marked nonblocking, and no space is available for the
sendto() function.
SEE ALSO
Functions: getsockopt(2), poll(2), recv(2), recvfrom(2), recvmsg(2),
select(2), send(2), sendmsg(2), setsockopt(2), shutdown(2), socket(2).
Standards: standards(5).
Network Programmer's Guide
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