send(2)
NAME
send, sendto, sendmsg − send a message from a socket
SYNTAX
#include <sys/types.h>
#include <sys/socket.h>
int cc = send(s, msg, len, flags)
char *msg;
int s, len, flags;
int cc = sendto(s, msg, len, flags, to, tolen)
char *msg;
int s, len, flags, tolen;
struct sockaddr *to;
int cc = sendmsg(s, msg, flags)
struct msghdr msg[];
int s, flags;
DESCRIPTION
The send, sendto, and sendmsg system calls are used to transmit a message to another socket. The send call can be used only when the socket is in a connected state, while the sendto and sendmsg calls can be used 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, then the error EMSGSIZE is returned, and the message is not transmitted.
No indication of failure to deliver is implicit in a send call. Return values of −1 indicate some locally detected errors.
If no messages space is available at the socket to hold the message to be transmitted, then send normally blocks, unless the socket has been placed in non-blocking I/O mode. The select call may be used to determine when it is possible to send more data.
The specified flags may be set to SOF_OOB to send “out-of-band” data on sockets which support this notion (for example, SOCK_STREAM).
For a description of the msghdr structure, see recv(2).
RETURN VALUE
If successful, these calls return the number of characters sent. If unsuccessful, they return a −1, and the global variable errno indicates the error code.
DIAGNOSTICS
The send, sendto, and sendmsg calls will fail if:
[EBADF] An invalid descriptor was specified.
[ENOTSOCK] The specified s is not a socket.
[EFAULT] An invalid user space address was specified for a parameter.
[EMSGSIZE] The socket requires that message be sent atomically, and the size of the message to be sent made this impossible.
[EWOULDBLOCK]
The socket is marked non-blocking, and the requested operation would block.