Question

I have next code:

int main()
{
 OwnSelect(23, FD_READ | FD_WRITE); // <---- Several arguments as one
 return 0;
}

int OwnSelect(SOCKET s, long lNetworkEvents)
{
 // How can i check that FD_READ has been passed?
 if(lNetworkEvents == FD_READ)
 {
  // never here
 }
 return 0;
}

How can i check that FD_READ has been passed no matter if another FD has been passed with FD_READ.
Thanks!

Answer 1

Seems like you’re missing out on a bit of basic bit manipulation here. You’re OR’ing FD_READ and FD_WRITE (| = bitwise OR), thereby setting the bits indicated by both values, as a parameter. To check if FD_READ was passed, you need to AND lNetworkEvents with FD_READ and check if the result equals FD_READ, like so:


if (FD_READ == (lNetworkEvents & FD_READ)) { ... }


This of course assuming that FD_READ and FD_WRITE are values that were meant to be used this way (i.e. typically don’t have overlapping bits).

edit: fixed, wabepper is absolutely right 🙂 oops!