Check if a socket is connected in mac os x - c++

Question

In Windows platform I can check if a socket is connected by this code:
bool isConnected(int socket)
{
int err;
int len = sizeof (err);
getsockopt(socket, SOL_SOCKET, SO_ERROR, (char*)&err, &len);
return err == 0;
}
In OS X this function always returns true.
What is the official way to do it?

Answer 1

This function works for both Windows and Mac platforms:
bool isConnected(int socket)
{
int err;
#ifdef __APPLE__
uint32_t len;
#elif _Windows
int len;
#endif
sockaddr_in addr;
len = sizeof (addr);
err = getpeername(socket, (sockaddr*)&addr, &len);
return err == 0;
}

Answer 2

The only way I know to determine if a blocking socket is connected is to perform an actual send/recv operation and check the result for error. On Windows, a non-blocking socket can also issue asynchronous notifications on socket activity, like FD_CLOSE for disconnects.
The one place SOL_ERROR comes in handy is for a non-blocking connect() call. After select() reports the connect operation is finished, SOL_ERROR can be used to determine whether connect() was successful or why it failed.

Answer 3

This - if (connect(s, (struct sockaddr *)&sa, sizeof sa) < 0) is close enough to winsock's isConnected.
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
int main() {
register int s;
register int bytes;
struct sockaddr_in sa;
char buffer[BUFSIZ+1];
if ((s = socket(PF_INET, SOCK_STREAM, 0)) < 0) {
perror("socket");
return 1;
}
bzero(&sa, sizeof sa);
sa.sin_family = AF_INET;
sa.sin_port = htons(13);
sa.sin_addr.s_addr = htonl((((((192 << 8) | 43) << 8) | 244) << 8) | 18);
if (connect(s, (struct sockaddr *)&sa, sizeof sa) < 0) {
perror("connect");
close(s);
return 2;
}
while ((bytes = read(s, buffer, BUFSIZ)) > 0)
write(1, buffer, bytes);
close(s);
return 0;
}