Re: [Boost-users] Ugly warnings from BOOST_STATIC_ASSERT

From: Ricardo Muñoz (rmunoz_at_[hidden])
Date: 2008-03-18 16:19:49

On Tue, Mar 18, 2008 at 6:31 PM, John Maddock <john_at_[hidden]> wrote:
> Jean-Francois Bastien wrote:
>  >> We have this really neat and simple macro in our project:
>  >> #define compile_assert(x) typedef bool
>  >> COMPILE_ASSERT[(x) ? 1 : -1]
>  >>
>  >> Although it does what we need and serves us well, I
>  >> tried to replace
>  >> it with BOOST_STATIC_ASSERT. Unfortunately this resulted
>  >> in a lot of
>  >> ugly warnings throughout the compile:
>  >>   warning: use of old-style cast
>  >>
>  >
>  > There's the following comment in the static assert header:
>  >
>  > // Note that the argument to the assert is explicitly cast to bool
>  > using old-
>  > // style casts: too many compilers currently have problems with
>  > static_cast
>  > // when used inside integral constant expressions.
>  >
>  > The solution would be to add even more defines to use old style or
>  > static casts depending on which compiler is used.
>
>  Right: historically this is why the header doesn't use static_cast here.
>
>  Unfortunately GCC appears to be one of the compilers that chokes if you use
>  static_cast in an integral constant expression: testing the diff below with
>  gcc-3.4 (cygwin) results in the tests failing (where as enabling the same
>  static_cast useage with msvc or intel does work OK).
>
>  If you anyone can test this with gcc-4.x and let me know which versions
>  might accept this patch OK that would be very useful, I'm attaching the
>  updated static_assert.hpp as well as the diff.

Hi!, hope this help:

ricardo_at_miles:~/devel$ cat foo_static.cpp
#include <boost/static_assert.hpp>

BOOST_STATIC_ASSERT(sizeof(int) >= sizeof(short));

int main()
{
  return 0;
}
ricardo_at_miles:~/devel$ svn info boost-trunk/
Path: boost-trunk
URL: http://svn.boost.org/svn/boost/trunk
Repository Root: http://svn.boost.org/svn/boost
Repository UUID: b8fc166d-592f-0410-95f2-cb63ce0dd405
Revision: 43710
Node Kind: directory
Schedule: normal
Last Changed Author: bemandawes
Last Changed Rev: 43709
Last Changed Date: 2008-03-18 20:35:18 +0100 (Tue, 18 Mar 2008)

ricardo_at_miles:~/devel$ gcc --version
gcc (GCC) 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

ricardo_at_miles:~/devel$ gcc foo_static.cpp -o foo_static -Wall
-Wold-style-cast -I./boost-trunk/
ricardo_at_miles:~/devel$

Regards,

>  John.
>
>  Here's the diff:
>
>  Index: C:/data/boost/boost/trunk/boost/static_assert.hpp
>  ===================================================================
>  --- C:/data/boost/boost/trunk/boost/static_assert.hpp (revision 43667)
>  +++ C:/data/boost/boost/trunk/boost/static_assert.hpp (working copy)
>  @@ -28,6 +28,17 @@
>   #  define BOOST_SA_GCC_WORKAROUND
>   #endif
>
>  +//
>  +// If the compiler supports the use of static_cast inside an integral
>  +// constant expression, and it issues warnings about old C style casts,
>  +// then enable this:
>  +//
>  +#if defined(__GNUC__) && ((__GNUC__ > 3) || ((__GNUC__ == 3) &&
>  (__GNUC_MINOR__ >= 4)))
>  +#define BOOST_STATIC_ASSERT_BOOL_CAST static_cast<bool>
>  +#else
>  +#define BOOST_STATIC_ASSERT_BOOL_CAST (bool)
>  +#endif
>  +
>   #ifdef BOOST_HAS_STATIC_ASSERT
>   #  define BOOST_STATIC_ASSERT( B ) static_assert(B, #B)
>   #else
>  @@ -78,14 +89,14 @@
>   #elif defined(BOOST_MSVC)
>   #define BOOST_STATIC_ASSERT( B ) \
>     typedef ::boost::static_assert_test<\
>  -      sizeof(::boost::STATIC_ASSERTION_FAILURE< (bool)( B ) >)>\
>  +      sizeof(::boost::STATIC_ASSERTION_FAILURE<
>  BOOST_STATIC_ASSERT_BOOL_CAST ( B ) >)>\
>           BOOST_JOIN(boost_static_assert_typedef_, __COUNTER__)
>   #elif defined(BOOST_INTEL_CXX_VERSION) || defined(BOOST_SA_GCC_WORKAROUND)
>   // agurt 15/sep/02: a special care is needed to force Intel C++ issue an
>  error
>   // instead of warning in case of failure
>   # define BOOST_STATIC_ASSERT( B ) \
>      typedef char BOOST_JOIN(boost_static_assert_typedef_, __LINE__) \
>  -        [ ::boost::STATIC_ASSERTION_FAILURE< (bool)( B ) >::value ]
>  +        [ ::boost::STATIC_ASSERTION_FAILURE<
>  BOOST_STATIC_ASSERT_BOOL_CAST( B ) >::value ]
>   #elif defined(__sgi)
>   // special version for SGI MIPSpro compiler
>   #define BOOST_STATIC_ASSERT( B ) \
>  @@ -100,12 +111,12 @@
>   #define BOOST_STATIC_ASSERT( B ) \
>     BOOST_STATIC_CONSTANT(int, \
>       BOOST_JOIN(boost_static_assert_test_, __LINE__) = \
>  -       sizeof(::boost::STATIC_ASSERTION_FAILURE< (bool)( B ) >) )
>  +       sizeof(::boost::STATIC_ASSERTION_FAILURE<
>  BOOST_STATIC_ASSERT_BOOL_CAST( B ) >) )
>   #else
>   // generic version
>   #define BOOST_STATIC_ASSERT( B ) \
>     typedef ::boost::static_assert_test<\
>  -      sizeof(::boost::STATIC_ASSERTION_FAILURE< (bool)( B ) >)>\
>  +      sizeof(::boost::STATIC_ASSERTION_FAILURE<
>  BOOST_STATIC_ASSERT_BOOL_CAST( B ) >)>\
>           BOOST_JOIN(boost_static_assert_typedef_, __LINE__)
>   #endif
>
>
> _______________________________________________
>  Boost-users mailing list
>  Boost-users_at_[hidden]
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>

-- 
Ricardo Muñoz
Warp Networks S.L. http://www.warp.es