SEND

Section: System Calls (2)
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BSD mandoc
BSD 4.2

NAME

send sendto sendmsg - send a message from a socket

SYNOPSIS

Fd #include <sys/types.h> Fd #include <sys/socket.h> Ft ssize_t Fn send int s const void *msg size_t len int flags Ft ssize_t Fn sendto int s const void *msg size_t len int flags const struct sockaddr *to int tolen Ft ssize_t Fn sendmsg int s const struct msghdr *msg int flags

DESCRIPTION

Fn Send , Fn sendto , and Fn sendmsg are used to transmit a message to another socket. Fn Send may be used only when the socket is in a connected state, while Fn sendto and Fn sendmsg may be used at any time.

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

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

If no messages space is available at the socket to hold the message to be transmitted, then Fn send normally blocks, unless the socket has been placed in non-blocking I/O mode. The select(2) call may be used to determine when it is possible to send more data.

The Fa flags parameter may include one or more of the following:

#define MSG_OOB        0x1  /* process out-of-band data */
#define MSG_DONTROUTE  0x4  /* bypass routing, use direct interface */

The flag MSG_OOB is used to 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 is usually used only by diagnostic or routing programs.

See recv(2) for a description of the Fa msghdr structure.

RETURN VALUES

The call returns the number of characters sent, or -1 if an error occurred.

ERRORS

Fn Send , Fn sendto , and Fn sendmsg fail if:

Bq Er EBADF: An invalid descriptor was specified.
Bq Er ENOTSOCK: The argument Fa s is not a socket.
Bq Er EFAULT: An invalid user space address was specified for a parameter.
Bq Er EMSGSIZE: The socket requires that message be sent atomically, and the size of the message to be sent made this impossible.
Bq Er EAGAIN: The socket is marked non-blocking and the requested operation would block.
Bq Er ENOBUFS: The system was unable to allocate an internal buffer. The operation may succeed when buffers become available.
Bq Er ENOBUFS: The output queue for a network interface was full. This generally indicates that the interface has stopped sending, but may be caused by transient congestion.

HISTORY

The Fn send function call appeared in BSD 4.2

This document was created by man2html, using the manual pages.
Time: 16:28:59 GMT, April 18, 2022