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 'clean' code would give such a warning since
it's structures which are defined by the system.
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

[Victor Bazarov]

Henrik Goldman wrote:

I'm seeing a weird problem on hp-ux (ia64) using g++ 4.1.1.
Have you tried news:gnu.g++.help ? If not, why not? If you have, what
did you find out?
Here below is a tiny bit of code which sets up the nessecary code for
doing a select():

fd_set fdread, fdwrite;
Are we supposed to know what 'fd_set' is?
FD_ZERO(&fdread);

FD_ZERO(&fdwrite);

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

FD_SET(m_IncomingSocket.GetSocket(), &fdwrite);
Those 'FD_' things look like macros. How are they defined?
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 'clean' code
What makes you believe the code is "'clean'"? What does it mean,
exactly?
would give such a warning
since it's structures which are defined by the system.
However perhaps someone could tell me what it actually means and
eventually how to solve it? My g++ optimization is O2.

If you haven't tried news:gnu.g++.help yet, go try it. Also, they
have an online forum (on their web site), IIRC. Don't discount it.
It's much more suitable for questions on a particular compiler's
behaviour than c.l.c++.

V
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