'\" et

.TH SENDTO "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH PROLOG

This manual page is part of the POSIX Programmer's Manual.

The Linux implementation of this interface may differ (consult

the corresponding Linux manual page for details of Linux behavior),

or the interface may not be implemented on Linux.

.SH NAME

sendto

\(em send a message on a socket

.SH SYNOPSIS

.LP

.nf

#include <sys/socket.h>

.P

ssize_t sendto(int \fIsocket\fP, const void *\fImessage\fP, size_t \fIlength\fP,

    int \fIflags\fP, const struct sockaddr *\fIdest_addr\fP,

    socklen_t \fIdest_len\fP);

.fi

.SH DESCRIPTION

The

\fIsendto\fR()

function shall send a message through a connection-mode or

connectionless-mode socket.

.P

If the socket is a connectionless-mode socket, the message shall be sent

to the address specified by

.IR dest_addr

if no pre-specified peer address has been set. If a peer address has

been pre-specified, either the message shall be sent to the address

specified by

.IR dest_addr

(overriding the pre-specified peer address), or the function shall

return \(mi1 and set

.IR errno

to

.BR [EISCONN] .

.P

If the socket is connection-mode,

.IR dest_addr

shall be ignored.

.P

The

\fIsendto\fR()

function takes the following arguments:

.IP "\fIsocket\fR" 12

Specifies the socket file descriptor.

.IP "\fImessage\fR" 12

Points to a buffer containing the message to be sent.

.IP "\fIlength\fR" 12

Specifies the size of the message in bytes.

.IP "\fIflags\fR" 12

Specifies the type of message transmission. Values of this argument

are formed by logically OR'ing zero or more of the following flags:

.RS 12 

.IP MSG_EOR 14

Terminates a record (if supported by the protocol).

.IP MSG_OOB 14

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.

.IP MSG_NOSIGNAL 14

Requests not to send the SIGPIPE signal if an attempt to send is made

on a stream-oriented socket that is no longer connected. The

.BR [EPIPE] 

error shall still be returned.

.RE

.IP "\fIdest_addr\fR" 12

Points to a

.BR sockaddr

structure containing the destination address. The length and format of

the address depend on the address family of the socket.

.IP "\fIdest_len\fR" 12

Specifies the length of the

.BR sockaddr

structure pointed to by the

.IR dest_addr

argument.

.P

If the socket protocol supports broadcast and the specified address is

a broadcast address for the socket protocol,

\fIsendto\fR()

shall fail if the SO_BROADCAST option is not set for the socket.

.P

The

.IR dest_addr

argument specifies the address of the target.

.P

The

.IR length

argument specifies the length of the message.

.P

Successful completion of a call to

\fIsendto\fR()

does not guarantee delivery of the message. A return value of \(mi1

indicates only locally-detected errors.

.P

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,

\fIsendto\fR()

shall block 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,

\fIsendto\fR()

shall fail.

.br

.P

The socket in use may require the process to have appropriate

privileges to use the

\fIsendto\fR()

function.

.SH "RETURN VALUE"

Upon successful completion,

\fIsendto\fR()

shall return the number of bytes sent. Otherwise, \(mi1 shall be

returned and

.IR errno

set to indicate the error.

.SH ERRORS

The

\fIsendto\fR()

function shall fail if:

.TP

.BR EAFNOSUPPORT

.br

Addresses in the specified address family cannot be used with this

socket.

.TP

.BR EAGAIN " or " EWOULDBLOCK

.br

The socket's file descriptor is marked O_NONBLOCK and the requested

operation would block.

.TP

.BR EBADF

The

.IR socket

argument is not a valid file descriptor.

.TP

.BR ECONNRESET

A connection was forcibly closed by a peer.

.TP

.BR EINTR

A signal interrupted

\fIsendto\fR()

before any data was transmitted.

.TP

.BR EMSGSIZE

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

requires.

.TP

.BR ENOTCONN

The socket is connection-mode but is not connected.

.TP

.BR ENOTSOCK

The

.IR socket

argument does not refer to a socket.

.TP

.BR EOPNOTSUPP

The

.IR socket

argument is associated with a socket that does not support one or more

of the values set in

.IR flags .

.TP

.BR 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 or SOCK_SEQPACKET and the MSG_NOSIGNAL flag is not set,

the SIGPIPE signal is generated to the calling thread.

.P

If the address family of the socket is AF_UNIX, then

\fIsendto\fR()

shall fail if:

.TP

.BR EIO

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

system.

.TP

.BR ELOOP

A loop exists in symbolic links encountered during resolution of the

pathname in the socket address.

.TP

.BR ENAMETOOLONG

.br

The length of a component of a pathname is longer than

{NAME_MAX}.

.TP

.BR ENOENT

A component of the pathname does not name an existing file or the

pathname is an empty string.

.TP

.BR ENOTDIR

A component of the path prefix of the pathname in the socket address

names an existing file that is neither a directory nor a symbolic link

to a directory, or the pathname in the socket address contains at

least one non-\c

<slash>

character and ends with one or more trailing

<slash>

characters and the last pathname component names an existing file that

is neither a directory nor a symbolic link to a directory.

.br

.P

The

\fIsendto\fR()

function may fail if:

.TP

.BR EACCES

Search permission is denied for a component of the path prefix; or

write access to the named socket is denied.

.TP

.BR EDESTADDRREQ

.br

The socket is not connection-mode and does not have its peer address

set, and no destination address was specified.

.TP

.BR EHOSTUNREACH

.br

The destination host cannot be reached (probably because the host is

down or a remote router cannot reach it).

.TP

.BR EINVAL

The

.IR dest_len

argument is not a valid length for the address family.

.TP

.BR EIO

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

system.

.TP

.BR EISCONN

A destination address was specified and the socket is already

connected.

.TP

.BR ENETDOWN

The local network interface used to reach the destination is down.

.TP

.BR ENETUNREACH

.br

No route to the network is present.

.TP

.BR ENOBUFS

Insufficient resources were available in the system to perform the

operation.

.TP

.BR ENOMEM

Insufficient memory was available to fulfill the request.

.P

If the address family of the socket is AF_UNIX, then

\fIsendto\fR()

may fail if:

.TP

.BR ELOOP

More than

{SYMLOOP_MAX}

symbolic links were encountered during resolution of the pathname in

the socket address.

.TP

.BR ENAMETOOLONG

.br

The length of a pathname exceeds

{PATH_MAX},

or pathname resolution of a symbolic link produced an intermediate

result with a length that exceeds

{PATH_MAX}.

.LP

.IR "The following sections are informative."

.SH "EXAMPLES"

None.

.SH "APPLICATION USAGE"

The

\fIselect\fR()

and

\fIpoll\fR()

functions can be used to determine when it is possible to send more

data.

.SH "RATIONALE"

None.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "\fIgetsockopt\fR\^(\|)",

.IR "\fIpoll\fR\^(\|)",

.IR "\fIpselect\fR\^(\|)",

.IR "\fIrecv\fR\^(\|)",

.IR "\fIrecvfrom\fR\^(\|)",

.IR "\fIrecvmsg\fR\^(\|)",

.IR "\fIsend\fR\^(\|)",

.IR "\fIsendmsg\fR\^(\|)",

.IR "\fIsetsockopt\fR\^(\|)",

.IR "\fIshutdown\fR\^(\|)",

.IR "\fIsocket\fR\^(\|)"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "\fB<sys_socket.h>\fP"

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 7, Copyright (C) 2013 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group.

(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the

event of any discrepancy between this version and the original IEEE and

The Open Group Standard, the original IEEE and The Open Group Standard

is the referee document. The original Standard can be obtained online at

http://www.unix.org/online.html .

Any typographical or formatting errors that appear

in this page are most likely

to have been introduced during the conversion of the source files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .