recv(2)recv(2)NAMErecv - Receive messages from connected sockets
SYNOPSIS
#include <sys/socket.h>
ssize_t recv(
int socket,
void *buffer,
size_t length,
int options );
[Tru64 UNIX] The following definition of the recv() function does not
conform to current standards and is supported only for backward compat‐
ibility (see standards(5)): #include <sys/socket.h>
int recv(
int socket,
char *buffer,
int length,
int options );
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
recv(): XNS4.0, XNS5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
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 options 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.
DESCRIPTION
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 truncated
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.
NOTES
[Tru64 UNIX] The recv() function is identical to the recvfrom() func‐
tion with a zero-valued address_len parameter, and to the read() func‐
tion if no options 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.
RETURN VALUES
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. Other‐
wise, the function returns a value of -1 and sets errno to indicate the
error.
ERRORS
If the recv() function fails, errno may be set to one of the following
values: The read() would cause the information label of the process to
float to an information level that is not dominated by the process's
sensitivity level. 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 option 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 options are not sup‐
ported for this socket type or protocol. The connection timed out dur‐
ing connection establishment or due to a transmission timeout on active
connection. The socket is marked nonblocking, and no data is waiting
to be received.
SEE ALSO
Functions: recvfrom(2), recvmsg(2), send(2), sendmsg(2), sendto(2),
select(2), shutdown(2), socket(2), read(2), write(2)
Standards: standards(5)
Network Programmer's Guide
recv(2)
