sendmsg()

Send a message and its header to a socket

Synopsis:

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

ssize_t sendmsg( int s,
                 const struct msghdr * msg,
                 int flags );

Arguments:

s

The descriptor for the socket; see socket().

msg

A pointer to the message that you want to send. For a description of the msghdr structure, see recvmsg().

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.

---

The tiny TCP/IP stack doesn't support MSG_OOB and MSG_DONTROUTE. For more information, see npm-ttcpip.so in the Utilities Reference.

---

Library:

libsocket

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

Description:

The sendmsg() 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 sendmsg() at any time.

No indication of failure to deliver is implicit in a sendmsg(). 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 sendmsg() 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:

EBADF

An invalid descriptor was specified.

EDESTADDRREQ

A destination address is required.

EFAULT

An invalid user space address was specified for a parameter.

EMSGSIZE

The socket requires that the message be sent atomically, but the size of the message made this impossible.

ENOBUFS

The system couldn't allocate an internal buffer. The operation may succeed when buffers become available.

ENOTSOCK

The argument s isn't a socket.

EWOULDBLOCK

The socket is marked nonblocking and the requested operation would block.

Classification:

POSIX 1003.1

See also:

getsockopt(), ioctl(), recv(), select(), send(), sendto(), socket(), write()