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

[Roland Bock <rbock@…>]

Hi,

compiling the attached example with gcc-4.4.3 (Ubuntu 10.4, 64bit) with

-Wall -O3

leads to a long warning message (second attachment), culminating in

boost/1.44/include/boost/function/function_base.hpp:321: warning: dereferencing type-punned pointer will break strict-aliasing rules
boost/1.44/include/boost/function/function_base.hpp:325: warning: dereferencing type-punned pointer will break strict-aliasing rules

A way to avoid this warning is been suggested by Justin in the boost-users mailing list:

​http://lists.boost.org/boost-users/2010/08/61564.php

Replace:

reinterpret_cast<functor_type*>(&in_buffer.data)->~Functor();

with:

functor_type* p = reinterpret_cast<functor_type*>(&in_buffer.data);
p->~Functor();

(Second line with out_buffer, respectively)

As noted by Emil Dotchevski in the thread on boost-users, it seems questionable why splitting up the original lines can get rid of the warning. So maybe a ticket should be filed for gcc by someone more knowledgeable than me.

[Roland Bock <rbock@…>]

Source code leading to said warning

[Roland Bock <rbock@…>]

Warning messages

[sergey.belyashov@…]

this is dublicate of Ticket #3780

[anonymous]

When will the patch be applied? This warning is very annoying to me because it causes pages of follow-up template errors. Is the suggested patch not considered a good fix to the problem?

[Peter Dimov]

Not sure who is maintaining function these days, let's try to volunteer Daniel James. :-)

[sergey.belyashov@…]

May be safer is to replace reinterpret_cast<functor_type*>(something) by static_cast<functor_type*>(static_cast<void*>(something))?

[Daniel James]

No thanks.

[Peter Dimov]

This is fixed by [62621] in trunk, and by [70361] in release.