Metrologic Optimus R, Руководство по программированию

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Chapter 3 Terminal Specific Function Library 155
recv
Purpose To receive data from a connected or bound socket.
Syntax int recv (SOCKET s, char *buf, int len, int flags);
s Descriptor identifying a connected socket
buf Pointer to the buffer in which data is received
len Maximum number of bytes to be received
flags MSG_OOB: process out-of-band data
MSG_PEEK: peek at incoming data
Example SOCKET s;
char buf[1024];
int len;
...................
if (socket_hasdata (s)) {
len = recv (s, buf, sizeof (buf), 0);
if (len < 0) {
printf ("recv fails on socket: %d", s);
...................
}
}
Description This routine reads incoming data from a specified buffer ( buf ) on a connected
socket.
The flags argument allows one of the following values:
MSG_OOB returns urgent data (out-of-bound data)
MSG_PEEK returns data but do not remove it from buffer,
allowing it to be read again on subsequent calls
The select() routine may be used to determine when more data arrives. (?)
Note that this is a blocking function. This routine will not return unless for the
following reason:
an error happens
data is received
the receive action times out
The application can avoid this blocking behavior by using socket_hasdata() to
make sure there is data available before calling recv().
Return
If successful, it returns a non-negative integer (>=0) indicating the number of
bytes received and stored into buffer.
On error, it returns -1.
The global variable errno is set to indicate the error condition encountered.