Receive a message from a socket
ssize_t recv( int s,
void * buf,
int flags );
- The descriptor for the socket; see
- A pointer to a buffer where the function can store the message.
- The size of the buffer.
- A combination formed by ORing one or more of the values:
- MSG_OOB — process out-of-band data.
This flag requests receipt of out-of-band data that wouldn't be
received in the normal data stream.
You can't use this flag with protocols that place expedited data at the
head of the normal data queue.
- MSG_PEEK — peek at the incoming message.
This flag causes the receive operation to return data from the
beginning of the receive queue without removing that data
from the queue. Thus, a subsequent receive call will return
the same data.
- MSG_WAITALL — wait for full request or error. This
flag requests that the operation block until the full
request is satisfied. But the call may still return less
data than requested if a signal is caught, if an error or
disconnect occurs, or if the next data to be received is of
a different type than that returned.
Use the -l socket option to
to link against this library.
The recv() function receives a message from a socket.
It's normally used only on a connected socket — see
— and is identical to
with a zero from parameter.
This routine returns the length of the message on
successful completion. If a message is too long for the
supplied buffer, buf, then excess bytes might be discarded,
depending on the type of socket that the message is received
If no messages are available at the socket, the receive call
waits for a message to arrive, unless the socket is
ioctl()—in which case
-1 is returned and the external variable
errno is set to EWOULDBLOCK. Normally, the
receive calls return any data available, up to the requested
amount, rather than wait for the full amount requested; this
behavior is affected by the socket-level options SO_RCVLOWAT
and SO_RCVTIMEO described in
You can use select() to determine when
more data is to arrive.
The number of bytes received, or -1 if an error occurs
(errno is set).
- Invalid descriptor s.
- The receive buffer is outside the
process's address space.
- The receive was interrupted by delivery of a signal
before any data was available.
- The socket is associated with a connection-oriented
protocol and hasn't been connected; see connect()
- Either the socket is marked nonblocking and the receive
operation would block, or a receive timeout had been set and
the timeout expired before data was received.