recvfrom()

The socket call receives data on a socket.

Syntax

#include <types.h>
#include <sys\socket.h>
int recvfrom(s, buf, len, flags, name, namelen)
int s;
char *buf;
int len;
int flags;
struct sockaddr *name;
int *namelen;

Parameters

s

Socket descriptor.

Pointer to the buffer that receives the data.

Length of the buffer in bytes pointed to by the buf parameter.

Permits the call to exercise control over the reception of messages. Set this parameter by specifying one or more of the following flags. If you specify more than one flag, use the logical OR operator (|) to separate them. Setting this parameter is supported only for sockets in the internet domain.

MSG_DONTWAIT

Do not wait for resources or data during this call.
MSG_OOB
Reads any out-of-band data on the socket.
MSG_PEEK
Peeks at the data present on the socket; the data is returned but not consumed, so that a subsequent receive operation sees the same data.
MSG_WAITALL
Wait for data to fill all buffers before returning.
name
Pointer to a sockaddr structure (buffer) that data is received from. If name is a nonzero value, the source address is returned.
namelen
Pointer to the size in bytes of the buffer pointed to by name.

Description

The recvfrom() call receives data on a socket with descriptor s and stores it in a buffer. The recvfrom() call applies to any socket type, whether connected or not.

If name is nonzero, the address of the data sender is returned. The namelen parameter is first initialized to the size of the buffer associated with name; on return, it is modified to indicate the actual number of bytes stored there.

The recvfrom() call returns the length of the incoming message or data. If a datagram or sequenced packet is too long to fit in the supplied buffer, the excess is discarded. No data is discarded for stream or sequenced packet sockets. If data is not available at the socket with descriptor s, the recvfrom() call waits for data to arrive and blocks the caller, unless the socket is in nonblocking mode. See ioctl() for a description of how to set nonblocking mode.

Return Values

When successful, the number of bytes of data received into the buffer is returned. The value -1 indicates an error. You can get the specific error code by calling sock_errno() or psock_errno().

Error Code

Description
SOCENOTSOCK
Thesparameterisnotavalidsocketdescriptor .
SOCEFAULT
Usingthebufandlenparameterswouldresultinanattempttoaccessmemoryoutsidethecaller ' saddressspace .
SOCEWOULDBLOCK
Thesparameterisinnonblockingmodeandnodataisavailabletoreceive ,ortheSO _ RCVTIMEOoptionhasbeensetforsocketsandthetimeoutexpiredbeforeanydataarrivedtoreceive .
SOCEINVAL
Invalidargument .

Related Calls

ioctl() readv()
recv()
recvmsg()
select()
send()
sendmsg()
sendto()
setsockopt()
shutdown()
sock_errno()
socket()
writev()

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