HP-UX Reference (11i v3 07/02) - 2 System Calls (vol 5)

r
recv(2) recv(2)
NAME
recv(), recvfrom(), recvmsg() - receive a message from a socket
SYNOPSIS
#include <sys/socket.h>
int recv(int s, void *buf, int len, int flags);
int recvfrom(
int s,
void *buf,
int len,
int flags,
void *from,
int *fromlen
);
int recvmsg(int s, struct msghdr msg[], int flags);
UNIX 03 Only (X/Open Sockets)
ssize_t recv(int s, void *buf, size_t len, int flags);
ssize_t recvfrom(
int s,
void *__restrict buf,
size_t len,
int flags,
struct sockaddr *__restrict from,
socklen_t *__restrict fromlen
);
ssize_t recvmsg(int s, struct msghdr *msg, int flags);
Obsolescent UNIX 95 Only (X/Open Sockets)
ssize_t recvfrom(
int s,
void *buf,
size_t len,
int flags,
struct sockaddr *from,
size_t *fromlen
);
DESCRIPTION
The recv(), recvfrom() , and recvmsg() system calls are used to receive messages from a socket.
s is a socket descriptor from which messages are received.
buf is a pointer to the buffer into which the messages are placed.
len is the maximum number of bytes that can fit in the buffer referenced by buf.
If the socket uses connection-based communications, such as a SOCK_STREAM socket, these calls can only
be used after the connection has been established (see connect(2)). For connectionless sockets such as
SOCK_DGRAM, these calls can be used whether a connection has been specified or not.
recvfrom() operates in the same manner as recv() except that it is able to return the address of the
socket from which the message was sent. For connected datagram sockets, recvfrom() simply returns
the same address as getpeername() (see getpeername(2)). For stream sockets, recvfrom() retrieves
data in the same manner as recv(), but does not return the socket address of the sender. If from is
nonzero, the source address of the message is placed in the socket address structure pointed to by from.
fromlen is a value-result parameter, initialized to the size of the structure associated with from, and
modified on return to indicate the actual size of the address stored there. If the memory pointed to by from
is not large enough to contain the entire address, only the first fromlen bytes of the address are returned.
For message-based sockets such as SOCK_DGRAM, the entire message must be read in a single operation.
If a message is too long to fit in the supplied buffer, the excess bytes are discarded. For stream-based sock-
ets such as SOCK_STREAM, there is no concept of message boundaries. In this case, data is returned to
HP-UX 11i Version 3: February 2007 − 1 − Hewlett-Packard Company 335