Type punned-pointers

[Henrik Goldman]

Hi,

I'm seeing a weird problem on hp-ux (ia64) using g++ 4.1.1.

Here below is a tiny bit of code which sets up the nessecary code for doing
a select():

fd_set fdread, fdwrite;

FD_ZERO(&fdread);

FD_ZERO(&fdwrite);

FD_SET(m_IncomingSocket.GetSocket(), &fdread);

FD_SET(m_IncomingSocket.GetSocket(), &fdwrite);

For the last two lines I get the following warning:

warning: dereferencing type-punned pointer will break strict-aliasing rules
warning: dereferencing type-punned pointer will break strict-aliasing rules

I don't really understand why this code would give such a warning since
it's structures which are defined by the system and I'm following what the 
man pages say.
However perhaps someone could tell me what it actually means and eventually
how to solve it? My g++ optimization is O2.

Thanks in advance.
-- Henrik