recv()

Receive a message from a socket

Synopsis:

#include <sys/types.h>
#include <sys/socket.h>

ssize_t recv( int s,
              void * buf,
              size_t len,
              int flags );

Arguments:

s
The descriptor for the socket; see socket().
buf
A pointer to a buffer where the function can store the message.
len
The size of the buffer.
flags
A combination formed by ORing one or more of the values:

Library:

libsocket

Use the -l socket option to qcc to link against this library.

Description:

The recv() function receives a message from a socket. It's normally used only on a connected socket — see connect() — and is identical to recvfrom() 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 from; see socket().

If no messages are available at the socket, the receive call waits for a message to arrive, unless the socket is nonblocking—see 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 getsockopt().

You can use select() to determine when more data is to arrive.

Returns:

The number of bytes received, or -1 if an error occurs (errno is set).

Errors:

EBADF
Invalid descriptor s.
EFAULT
The receive buffer is outside the process's address space.
EINTR
The receive was interrupted by delivery of a signal before any data was available.
ENOTCONN
The socket is associated with a connection-oriented protocol and hasn't been connected; see connect() and accept().
EWOULDBLOCK
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.

Classification:

POSIX 1003.1

Safety:
Cancellation point Yes
Interrupt handler No
Signal handler No
Thread Yes

See also:

connect(), ioctl(), getsockopt(), read(), recvfrom(), recvmsg(), select(), socket()