Re: [boost] BOOST_STATIC_WARNING ?

From: Robert Ramey (ramey_at_[hidden])
Date: 2003-06-17 01:34:01

John Maddok wrote:
>Another problem (I think) is that with BOOST_STATIC_ASSERT you know compilation will stop.

>However, a BOOST_STATIC_WARNING would keep re-apearing in each translation unit #including your file:

>// boost_file.hpp

>BOOST_STATIC_WARNING( "we're in boost_file.hpp")

>// file1.hpp
>#include <boost/boost_file.hpp>

>-- appears here

>// file2.hpp 
>#include <boost/boost_file.hpp>

a) BOOST_STATIC_WARNING only appears once since include files are guarded by
#ifdef ....
#define
...
#endif

BOOST_STATIC_ASSERT doesn't stop compilation.  It only appears once for the
same reason that BOOST_STATIC_WARNING does.

Here is my best effort at BOOST_STATIC_WARNING.

It suffers from the followng deficiencies:

a) On a Microsoft platform it only works within a function definition.
b) It gives a warning that points to the exact line, BUT doesn't have a particularly eye catching message

Other than that, it seems to work as one would hope.

Robert Ramey

//  (C) Copyright Robert Ramey 2003.
//  Permission to copy, use, modify, sell and
//  distribute this software is granted provided this copyright notice appears
//  in all copies. This software is provided "as is" without express or implied
//  warranty, and with no claim as to its suitability for any purpose.

//  See http://www.boost.org/libs/static_assert for documentation.

/*
 Revision history:
   15 June 2003
      Initial version.
*/

#ifndef BOOST_STATIC_WARNING_HPP
#define BOOST_STATIC_WARNING_HPP

#include <boost/config.hpp>
namespace boost { 

// used to generate warning
template<const char *T> struct WARNING_MESSAGE;

template<bool>
class STATIC_WARNING;

template<>
class STATIC_WARNING<false>
{
        typedef char type;
};

template<>
class STATIC_WARNING<true>
{
        typedef int type;
};

} // boost

// Implemenation
// this implementation relies on the warning issued by compilers
// when a constant is truncated.  If the boolean is false, the
// compiler emits a warning message.  The warning message points
// to the point where the macro was invoked.  The warning message
// indicates data lost in an integral conversion.  Unfortunately,
// we have yet to discover an way to invoke a more eye catching
// warning message a la BOOST_STATIC_ASSERT.

#if defined(BOOST_MSVC)
// __LINE__ macro broken when -ZI is used see Q199057
// Sooo for this compiler this only works inside a function
#define BOOST_STATIC_WARNING(B) \
{static_cast< ::boost::STATIC_WARNING< (bool)(B) >::type >(0xffff);}
#else
#define BOOST_STATIC_WARNING(B) \
enum { \
        BOOST_JOIN(boost_static_warning_enum_, __LINE__) \
        = static_cast< ::boost::STATIC_WARNING< (bool)(B) >::type >(0xffff) \
}
#endif

#endif // BOOST_STATIC_WARNING_HPP

/////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
// test_static_warning.cpp:

// (C) Copyright 2002 Robert Ramey - http://www.rrsd.com . Permission to copy, 
// use,	modify,	sell and distribute	this software is granted provided this
// copyright notice	appears	in all copies. This	software is	provided "as is"
// without express or implied warranty,	and	with no	claim as to	its	suitability
// for any purpose.

#include <boost/static_warning.hpp>

#if ! defined(BOOST_MSVC)
BOOST_STATIC_WARNING(false);
BOOST_STATIC_WARNING(true);
#endif

int
test_main( int argc, char* argv[] )
{
        BOOST_STATIC_WARNING(true);
        BOOST_STATIC_WARNING(false);
        return 0;
}