The recv() function shall receive a message from a connection-mode or
connectionless-mode socket. It is normally used with connected sockets because
it does not permit the application to retrieve the source address of received
The recv() function takes the following arguments:
Specifies the socket file descriptor.
Points to a buffer where the message should be stored.
Specifies the length in bytes of the buffer pointed to by
the buffer argument.
Specifies the type of message reception. Values of this
argument are formed by logically OR'ing zero or more of the following
Peeks at an incoming message. The data is
treated as unread and the next recv() or similar function shall still
return this data.
Requests out-of-band data. The significance
and semantics of out-of-band data are protocol-specific.
On SOCK_STREAM sockets this requests that the
function block until the full amount of data can be returned. The function may
return the smaller amount of data if the socket is a message-based socket, if
a signal is caught, if the connection is terminated, if MSG_PEEK was
specified, or if an error is pending for the socket.
The recv() function shall return the length of the message written to the
buffer pointed to by the buffer argument. For message-based sockets,
such as SOCK_DGRAM and SOCK_SEQPACKET, the entire message shall be read in a
single operation. If a message is too long to fit in the supplied buffer, and
MSG_PEEK is not set in the flags argument, the excess bytes shall be
discarded. For stream-based sockets, such as SOCK_STREAM, message boundaries
shall be ignored. In this case, data shall be returned to the user as soon as
it becomes available, and no data shall be discarded.
If the MSG_WAITALL flag is not set, data shall be returned only up to the end of
the first message.
If no messages are available at the socket and O_NONBLOCK is not set on the
socket's file descriptor, recv() shall block until a message arrives.
If no messages are available at the socket and O_NONBLOCK is set on the
socket's file descriptor, recv() shall fail and set errno to
[EAGAIN] or [EWOULDBLOCK].
Upon successful completion, recv() shall return the length of the message
in bytes. If no messages are available to be received and the peer has
performed an orderly shutdown, recv() shall return 0. Otherwise, -1
shall be returned and errno set to indicate the error.
The socket's file descriptor is marked O_NONBLOCK and no data is waiting to
be received; or MSG_OOB is set and no out-of-band data is available and
either the socket's file descriptor is marked O_NONBLOCK or the socket
does not support blocking to await out-of-band data.
The socket argument is not a valid file
A connection was forcibly closed by a peer.
The recv() function was interrupted by a signal that
was caught, before any data was available.
The MSG_OOB flag is set and no out-of-band data is
A receive is attempted on a connection-mode socket that is
The socket argument does not refer to a socket.
The specified flags are not supported for this socket type
The connection timed out during connection establishment,
or due to a transmission timeout on active connection.
The recv() function may fail if:
An I/O error occurred while reading from or writing to the
Insufficient resources were available in the system to
perform the operation.
Insufficient memory was available to fulfill the request.
The recv() function is equivalent to recvfrom() with a zero
address_len argument, and to read() if no flags are used.
The select() and poll() functions can be used to determine when
data is available to be received.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html