sendto()

Send a message to a socket at a specific address

Synopsis:

#include <sys/types.h>
#include <sys/socket.h>

ssize_t sendto( int s,
                const void * msg,
                size_t len,
                int flags,
                const struct sockaddr * to,
                socklen_t tolen );

Arguments:

s
The descriptor for the socket; see socket() .
msg
A pointer to the message that you want to send.
len
The length of the message.
flags
A combination of the following:
  • MSG_OOB — process out-of-band data. Use this bit when you send "out-of-band" data on sockets that support this notion (e.g. SOCK_STREAM). The underlying protocol must also support out-of-band data.
  • MSG_DONTROUTE — bypass routing; create a direct interface. You normally use this bit only in diagnostic or routing programs.
  • MSG_NOSIGNAL — don't raise a SIGPIPE signal when the other end breaks the connection.
to
A pointer to a sockaddr object that specifies the address of the target.
tolen
A socklen_t object that specifies the size of the to address.

Library:

libsocket

Use the -l socket option to qcc to link against this library.

Description:

The sendto() function is used to transmit a message to another socket. You can use send() only when the socket is in a connected state; you can use sendto() at any time.

The address of the target is given by to, with tolen specifying its size. The length of the message is given by len. If the message is too long to pass atomically through the underlying protocol, the error EMSGSIZE is returned, and the message isn't transmitted.

No indication of failure to deliver is implicit in a sendto(). Locally detected errors are indicated by a return value of -1.

If no message space is available at the socket to hold the message to be transmitted, then sendto() normally blocks, unless the socket has been placed in nonblocking I/O mode. You can use select() to determine when it's possible to send more data.

Returns:

The number of bytes sent, or -1 if an error occurs ( errno is set).

Errors:

EACCES
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 can't be used with this socket.
EAGAIN
The socket's file descriptor is marked O_NONBLOCK, and the requested operation would block.
EBADF
An invalid descriptor was specified.
ECONNRESET
A connection was forcibly closed by a peer.
EDESTADDRREQ
The socket isn't connection-mode and doesn't have its peer address set, and no destination address was specified.
EFAULT
An invalid user space address was specified for a parameter.
EHOSTUNREACH
The destination host can't be reached (probably because the host is down or a remote router can't reach it).
EINTR
A signal interrupted sendto() before any data was transmitted.
EINVAL
The tolen argument isn't a valid length for the address family.
EIO
An I/O error occurred while reading from or writing to the filesystem.
EISCONN
A destination address was specified and the socket is already connected. This error may or may not be returned for connection mode sockets.
EMSGSIZE
The socket requires that the message be sent atomically, but the size of the message made this impossible.
ENETDOWN
The local network interface used to reach the destination is down.
ENETUNREACH
No route to the network is present.
ENOBUFS
The system couldn't allocate an internal buffer. The operation may succeed when buffers become available.
ENOMEM
Insufficient memory was available to fulfill the request.
ENOTCONN
The socket is connection-mode but isn't connected.
ENOTSOCK
The argument s isn't a socket.
EOPNOTSUPP
The s argument is associated with a socket that doesn't 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, a SIGPIPE signal is generated to the calling thread.
EWOULDBLOCK
The socket is marked nonblocking and the requested operation would block.

If the address family of the socket is AF_UNIX, sendto() fails if:

EIO
An I/O error occurred while reading from or writing to the filesystem.
ELOOP
A loop exists in symbolic links encountered during the resolution of the pathname in the socket address, or more than SYMLOOP_MAX symbolic links were encountered during the resolution of the pathname in the socket address.
ENAMETOOLONG
A component of a pathname exceeded NAME_MAX characters, or an entire pathname exceeded PATH_MAX characters, or pathname resolution of a symbolic link produced an intermediate result whose length exceeds PATH_MAX.
ENOENT
A component of the pathname doesn't 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 isn't a directory.

Classification:

POSIX 1003.1

Safety:  
Cancellation point Yes
Interrupt handler No
Signal handler No
Thread Yes

Last modified: 2013-12-23

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