NAME

sendto - send a message on a socket

SYNOPSIS

cc [ flag... ] file... -lxnet [ library ... ]
#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);

DESCRIPTION

The sendto() function sends a message through a connection-mode or connectionless-mode socket. If the socket is connectionless-mode, the message will be sent to the address specified by dest_addr. If the socket is connection-mode, dest_addr is ignored.

If the socket protocol supports broadcast and the specified address is a broadcast address for the socket protocol, sendto() will fail if the SO_BROADCAST option is not set for the socket.

The dest_addr argument specifies the address of the target. The length argument specifies the length of the message.

Successful completion of a call to sendto() does not guarantee delivery of the message. A return value of −1 indicates only locally-detected errors.

If space is not available at the sending socket to hold the message to be transmitted and the socket file descriptor does not have O_NONBLOCK set, sendto() blocks until space is available. If space is not available at the sending socket to hold the message to be transmitted and the socket file descriptor does have O_NONBLOCK set, sendto() will fail.

The socket in use may require the process to have appropriate privileges to use the sendto() function.

PARAMETERS

The function takes the following arguments:

socket

Specifies the socket file descriptor.

message

Points to a buffer containing the message to be sent.

length

Specifies the size of the message in bytes.

flags

Specifies the type of message transmission. Values of this argument are formed by logically OR'ing zero or more of the following flags:

MSG_EOR

Terminates a record (if supported by the protocol)

MSG_OOB

Sends out-of-band data on sockets that support out-of-band data. The significance and semantics of out-of-band data are protocol-specific.

MSG_NOSIGNAL

Don't generate the SIGPIPE signal when a stream-oriented socket is no longer connected.

dest_addr

Points to a sockaddr structure containing the destination address. The length and format of the address depend on the address family of the socket.

dest_len

Specifies the length of the sockaddr structure pointed to by the dest_addr argument.

USAGE

The select(3C) and poll(2) functions can be used to determine when it is possible to send more data.

RETURN VALUES

Upon successful completion, sendto() returns the number of bytes sent. Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

In addition to the errors documented below, an asynchronous error generated by the underlying socket protocol may be returned. For the full list of errors, please see the corresponding socket protocol manual page. For example, for a list of TCP errors, please see tcp(4P).

The sendto() function will fail if:

EAFNOSUPPORT

Addresses in the specified address family cannot be used with this socket.

EAGAIN
EWOULDBLOCK

The socket's file descriptor is marked O_NONBLOCK and the requested operation would block.

EBADF

The socket argument is not a valid file descriptor.

ECONNRESET

A connection was forcibly closed by a peer.

EFAULT

The message or destaddr parameter cannot be accessed.

EINTR

A signal interrupted sendto() before any data was transmitted.

EMSGSIZE

The message is too large to be sent all at once, as the socket requires.

ENOTCONN

The socket is connection-mode but is not connected.

ENOTSOCK

The socket argument does not refer to 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-mode and is no longer connected. In the latter case, and if the socket is of type SOCK_STREAM, the SIGPIPE signal is generated to the calling thread unless the MSG_NOSIGNAL flag is set.

If the address family of the socket is AF_UNIX, then sendto() will fail if:

EIO

An I/O error occurred while reading from or writing to the file system.

ELOOP

Too many symbolic links were encountered in translating the pathname in the socket address.

ENAMETOOLONG

A component of a pathname exceeded NAME_MAX characters, or an entire pathname exceeded PATH_MAX characters.

ENOENT

A component of the pathname does not name an existing file or the pathname is an empty string.

ENOTDIR

A component of the path prefix of the pathname in the socket address is not a directory.

The sendto() function may fail if:

EACCES

Search permission is denied for a component of the path prefix; or write access to the named socket is denied.

EDESTADDRREQ

The socket is not connection-mode and does not have its peer address set, and no destination address was specified.

EHOSTUNREACH

The destination host cannot be reached (probably because the host is down or a remote router cannot reach it).

EINVAL

The dest_len argument is not a valid length for the address family.

EIO

An I/O error occurred while reading from or writing to the file system.

EISCONN

A destination address was specified and the socket is already connected.

ENETDOWN

The local interface used to reach the destination is down.

ENETUNREACH

No route to the network is present.

ENOBUFS

Insufficient resources were available in the system to perform the operation.

ENOMEM

Insufficient memory was available to fulfill the request.

ENOSR

There were insufficient STREAMS resources available for the operation to complete.

If the address family of the socket is AF_UNIX, then sendto() may fail if:

ENAMETOOLONG

Pathname resolution of a symbolic link produced an intermediate result whose length exceeds PATH_MAX.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Standard
MT-Level	MT-Safe