Linux - ioctl with FIONREAD always 0

Question

I\'m trying to get to know how many bytes there are readable at my TCP socket. I am calling ioctl with the Flag \"FIONREAD\" which should actually give me this value. When I ca

Answer 1

It's happening very quickly, that's why you don't see anything. What you're doing:

• ioctl: Is there data for me ? No, nothing yet
• recv: Block until there is data for me. Some (short) time later: Here is your data

So if you really want to see FIONREAD, just wait for it.

/* Try FIONREAD until we get *something* or ioctl fails. */
while (!bytesAv && ioctl (m_Socket,FIONREAD,&bytesAv) >= 0)
    sleep(1);