Sends gathered bytes through a socket to any other socket. Format #include <types.h> #include <socket.h> int sendmsg ( int s, struct msghdr *msg, int flags ); (BSD Version 4.4) int sendmsg ( int s, struct omsghdr *msg, int flags ); (BSD Version 4.3)
1 – Arguments
s A socket descriptor created with the socket() function. msg A pointer to a msghdr structure containing the message to be sent. The msg_iov field of the msghdr structure is used as a series of buffers from which data is read in order until msg_iovlen bytes have been obtained. flags Can be either 0 or MSG_OOB. If it is equal to MSG_OOB, the data is sent out of band. Data can be received before other pending data on the receiving socket if the receiver specifies a flag of MSG_OOB.
2 – Description
This function sends the data in a msghdr structure to any other socket. You can use this function on any socket to send data to any named socket. The data in the msg_iov field of the msghdr structure is sent to the socket whose address is specified in the msg_name field of the structure. The receiving socket gets the data using the read(), recv(), recvfrom(), or recvmsg() function. When the iovec array specifies more than one buffer, the data is gathered from all specified buffers before being sent. Normally the sendmsg() function blocks if there is no space for the incoming data in the buffer. It waits until the buffer space becomes available. If the socket is set to nonblocking and there is no space for the data, the sendmsg() function fails with the EWOULDBLOCK error. If the message is too large to be sent in one piece, and the socket type is SOCK_DGRAM, which requires that messages be sent in one piece, sendmsg() fails with the EMSGSIZE error. If the address specified is an INADDR_BROADCAST address, the SO_BROADCAST socket option must be set and the process must have OPER, SYSPRV, or BYPASS privilege for the I/O operation to succeed. A success return from sendmsg() does not guarantee that the data has been received by the peer. All errors (except EWOULDBLOCK) are detected locally. To determine when it is possible to send more data, use the select() function. Related Functions See also read(), recv(), recvfrom(), recvmsg(), socket(), and getsockopt().
3 – Return Values
n The number of bytes sent. -1 Error; errno is set to indicate the error.
4 – Errors
ENOTSOCK The socket descriptor is invalid. EFAULT An invalid user space address is specified for an argument. EMSGSIZE The socket requires that messages be sent atomically, but the size of the message to be sent makes this impossible. EWOULDBLOCK Blocks if the system does not have enough space for buffering the user data.