cc [ flag ... ] file ... -lsocket -lnsl [ library ... ] #include <sys/types.h> #include <sys/socket.h> #include <sys/uio.h>ssize_t recv(int s, void *buf, size_t len, int flags);
recv(), recvfrom(), and recvmsg() are used to receive messages from another socket. recv() may be used only on a connected socket (see connect(3SOCKET)), while recvfrom() and recvmsg() may be used to receive data on a socket whether it is in a connected state or not. s is a socket created with socket(3SOCKET).
If from is not a NULL pointer, the source address of the message is filled in. fromlen is a value-result parameter, initialized to the size of the buffer associated with from, and modified on return to indicate the actual size of the address stored there. The length of the message is returned. If a message is too long to fit in the supplied buffer, excess bytes may be discarded depending on the type of socket the message is received from (see socket(3SOCKET)).
If no messages are available at the socket, the receive call waits for a message to arrive, unless the socket is nonblocking (see fcntl(2)) in which case -1 is returned with the external variable errno set to EWOULDBLOCK.
The select() call may be used to determine when more data arrives.
The flags parameter is formed by ORing one or more of the following:
Read any “out-of-band” data present on the socket rather than the regular “in-band” data.
“Peek” at the data present on the socket; the data is returned, but not consumed, so that a subsequent receive operation will see the same data.
caddr_t msg_name; /* optional address */ int msg_namelen; /* size of address */ struct iovec *msg_iov; /* scatter/gather array */ int msg_iovlen; /* # elements in msg_iov */ caddr_t msg_accrights; /* access rights sent/received */ int msg_accrightslen;
Here msg_name and msg_namelen specify the destination address if the socket is unconnected; msg_name may be given as a NULL pointer if no names are desired or required. The msg_iov and msg_iovlen describe the scatter-gather locations, as described in read(2). A buffer to receive any access rights sent along with the message is specified in msg_accrights, which has length msg_accrightslen.
These calls return the number of bytes received, or -1 if an error occurred.
The calls fail if:
s is an invalid file descriptor.
The operation was interrupted by delivery of a signal before any data was available to be received.
An I/O error occurred while reading from or writing to the file system.
There was insufficient user memory available for the operation to complete.
There were insufficient STREAMS resources available for the operation to complete.
s is not a socket.
A stale NFS file handle exists.
The socket is marked non-blocking and the requested operation would block.
See attributes(5) for descriptions of the following attributes:
|ATTRIBUTE TYPE||ATTRIBUTE VALUE|