sendto(2) System Calls Manual sendto(2)
sendto - Sends messages through a socket
ssize_t sendto ( int socket, const void *message, size_t length, int flags, const struct sockaddr *dest_addr,
[POSIX] The definition of the sendto() function in POSIX.1g Draft 6.6 uses a socklen_t data type for the dest_len parameter instead of a
size_t data type as specified in XNS4.0 (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)):
int sendto ( int socket, char *message_addr, int length, int flags, struct sockaddr *dest_addr, int dest_len
Interfaces documented on this reference page conform to industry standards as follows:
Refer to the standards(5) reference page for more information about industry standards and associated tags.
Specifies the file descriptor for the socket. Points to the address containing the message to be sent. Specifies the size of the message
in bytes. Allows the sender to control the message transmission. The flags value to send a call is formed by logically ORing the follow-
ing values, defined in the sys/socket.h file: Terminates a record (if supported by the protocol). Processes out-of-band data on sockets
that support out-of-band data. [Tru64 UNIX] Sends without using routing tables. (Not recommended; for debugging purposes only.) Points
to a sockaddr structure, the format of which is determined by the domain and by the behavior requested for the socket. The sockaddr struc-
ture is an overlay for a sockaddr_in or sockaddr_un 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 sock-
addr 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. Specifies the length of the sockaddr
structure pointed to by the dest_addr parameter.
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 nonblock-
ing I/O mode.
Use the select() and poll() functions to determine when to send more data.
Upon successful completion, the sendto() function returns the number of characters sent. Otherwise, a value of -1 is returned, and errno
is set to indicate the error.
If the sendto() function fails, errno may be set to one of the following values: Search permission is denied for a component of the path
prefix; or write access to the named socket is denied. Addresses in the specified address family cannot be used with this socket. The
socket parameter is not valid. A connection was forcibly closed by a peer. You did not specify a destination address for the connection-
less socket that also did not have its peer address set. The message or dest_addr parameter is not in a writable part of the user address
space. The destination host is not reachable. A signal interrupted sendto before any data was transmitted. The dest_len parameter is not
a valid size for the specified address family. For an AF_UNIX socket, an I/O error occurred while reading from or writing to the file sys-
tem. The connection-oriented socket for which a destination address was specified is already connected. For an AF_UNIX socket, too many
symbolic links were encountered in translating the pathname in the socket address. The message is too large to be sent all at once, as the
socket requires. For an AF_UNIX socket, a component of the pathname exceeded NAME_MAX characters, or an entire pathname exceeded PATH_MAX
characters. The local network connection is not operational. The destination network is unreachable. Insufficient resources are avail-
able 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. For an AF_UNIX socket, a component of the path-
name does not name an existing file or the pathname is an empty string. The system did not have sufficient memory to fulfill the
request. The available STREAMS resources were insufficient for the operation to complete. The socket is connection-oriented but is
not connected. For an AF_UNIX socket, a component of the path prefix of the pathname in address is not a directory. The socket
parameter refers to a file, not a socket. The socket argument is associated with a socket that does not support one or more of the
values set in flags. 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.
The socket is marked nonblocking, and no space is available for the sendto() function.
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). delim off