Re: pointer casts(newbie)

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Tue, 10 Feb 2009 00:55:36 -0800 (PST)
Message-ID:
<063eefd6-3e09-497c-b859-c4a9577716d5@o36g2000yqh.googlegroups.com>
On Feb 9, 4:38 pm, Kai-Uwe Bux <jkherci...@gmx.net> wrote:

James Kanze wrote:


    [...]

If you cast it to a character type, you can access the
individual bytes. Modifying them will result in undefined
behavior if you later try to use the object with its
original type, but something like:

    template< typename T >
    void
    dump(
        std::ostream& dest,
        T const& obj )
    {
        IOSave saver( dest ) ;
        dest.setf( std::ios::hex, std::ios::basefield ) ;
        dest.fill( '0' ) ;
        unsigned char const*current
            = reinterpret_cast< unsigned char const* >( &obj ) ;
        unsigned char const*end = current + sizeof( T ) ;
        while ( current != end ) {
            dest << std::setw( 2 ) << *current ;
            ++ current ;
            if ( current != end ) {
                dest << ' ' ;
            }
        }
    }

is sometimes useful (and has fully defined behavior).


Nice. I agree that it is sometimes useful to read the
underlying bytes of an object.


Just one additional note: in my toolkit, this is present as a
class, with an overloaded <<, and a simple function which
returns an instance of the class (for type deduction), so you
can write things like:

    std::cerr << "x = " << dump( x ) << std::endl ;

Useful for debugging very low-level objects.

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