recv(2) System Calls Manual recv(2)
recv - Receives messages from connected sockets
ssize_t recv ( int socket, void *buffer, size_t length, int flags );
[Tru64 UNIX] The following definition of the recv() function does not conform to current standards and is supported only for backward com-
patibility (see standards(5)):
int recv ( int socket, char *buffer, int length, int flags );
Interfaces documented on this reference page conform to industry standards as follows:
Refer to the standards(5) reference page for more information about industry standards and associated tags.
Specifies the socket descriptor. Points to a buffer where the message should be placed. Specifies the size of the buffer pointed to by
the buffer parameter. Points to a value controlling the message reception. The flags parameter is formed by logically ORing one or more
of the following values, defined in the sys/socket.h file: Peek at incoming message. The data is treated as unread and the next recv()
function (or similar function) will still return this data. Process out-of-band data. Requests that the function block wait until the
full amount of data requested can be returned. The function may return a smaller amount of data if a signal is caught, the connection is
terminated, or an error is pending for the socket.
The recv() function receives messages from a connected socket. The recvfrom() and recvmsg() functions receive messages from both connected
and unconnected sockets; however, they are usually used for unconnected sockets only.
The recv() function returns the length of the message. If a message is too long to fit in the supplied buffer, excess bytes may be trun-
cated depending on the type of socket that issued the message.
If no messages are available at the socket, the recv() function waits for a message to arrive, unless the socket is nonblocking. If a
socket is nonblocking, errno is set to [EWOULDBLOCK].
Use the select() function to determine when more data arrives.
[Tru64 UNIX] The recv() function is identical to the recvfrom() function with a zero-valued address_len parameter, and to the read() func-
tion if no flags are used. For that reason the recv() function is disabled when 4.4BSD behavior is enabled; that is, when the _SOCK-
ADDR_LEN compile-time option is defined.
Upon successful completion, the recv() function returns the length of the message in bytes. If no messages are available and the peer has
closed the connection, the recv() function returns a value of 0. Otherwise, the function returns a value of -1 and sets errno to indicate
If the recv() function fails, errno may be set to one of the following values: The socket parameter is not valid. A connection was
forcibly closed by a peer. The data was directed to be received into a nonexistent or protected part of the process address space. The
buffer parameter is invalid. A signal interrupted the recv() function before any data was available. The MSG_OOB flag is set and no out-
of-band data is available. An I/O error occurred while reading from or writing to the file system. Insufficient resources were available
in the system to complete the call. The system did not have sufficient memory to fulfill the request. The available STREAMS resources
were insufficient for the operation to complete.
Receive is attempted on a connection-oriented socket that is not connected. The socket parameter refers to a file, not a socket. The
specified flags are not supported for this socket type or protocol. The connection timed out during connection establishment or due to a
transmission timeout on active connection. The socket is marked nonblocking, and no data is waiting to be received.
Functions: recvfrom(2), recvmsg(2), send(2), sendmsg(2), sendto(2), select(2), shutdown(2), socket(2), read(2), write(2)
Standards: standards(5) delim off