#include <sys/types.h> #include <sys/socket.h>
int recv(s, buf, len, flags) int s; char *buf; int len, flags;
int recvfrom(s, buf, len, flags, from, fromlen) int s; char *buf; int len, flags; struct sockaddr *from; int *fromlen;
int recvmsg(s, msg, flags) int s; struct msghdr *msg; int flags;
s is a socket created with socket.2 recv(), recvfrom(), and recvmsg() are used to receive messages from another socket. recv() may be used only on a connected socket (see connect.2 while recvfrom() and recvmsg() may be used to receive data on a socket whether it is in a connected state or not.
If from is not a NULL pointer, the source address of the message is filled in. fromlen is a value-result parameter, initialized to the size of the buffer associated with from, and modified on return to indicate the actual size of the address stored there. The length of the message is returned. If a message is too long to fit in the supplied buffer, excess bytes may be discarded depending on the type of socket the message is received from (see socket.2
If no messages are available at the socket, the receive call waits for a message to arrive, unless the socket is non-blocking (see ioctl.2 in which case -1 is returned with the external variable errno set to EWOULDBLOCK.
The select.2 call may be used to determine when more data arrive.
If the process calling recv(), recvfrom() or recvmsg() receives a signal before any data are available, the system call is restarted unless the calling process explicitly set the signal to interrupt these calls using sigvec() or sigaction() (see the discussions of SV_INTERRUPT on sigvec.2 and SA_INTERRUPT on sigaction.3v
The flags parameter is formed by ORing one or more of the following:
call uses a
structure to minimize the number of directly supplied parameters.
This structure is defined in
and includes the following members:
caddr_t msg_name; /* optional address */ int msg_namelen; /* size of address */ struct iovec *msg_iov; /* scatter/gather array */ int msg_iovlen; /* # elements in msg_iov */ caddr_t msg_accrights; /* access rights sent/received */ int msg_accrightslen;
Here msg_name and msg_namelen specify the destination address if the socket is unconnected; msg_name may be given as a NULL pointer if no names are desired or required. The msg_iov and msg_iovlen describe the scatter-gather locations, as described in read.2v A buffer to receive any access rights sent along with the message is specified in msg_accrights, which has length msg_accrightslen.
These calls return the number of bytes received, or -1 if an error occurred.
Created by unroff & hp-tools. © by Hans-Peter Bischof. All Rights Reserved (1997).
Last modified 21/April/97