In article <3829D761.FC5D91B5@quidsoft.se>,
  Dag Henriksson <dag.henriksson@quidsoft.se> wrote:
>
>
> Andrei Alexandrescu wrote:
>
> > Valentin Bonnard <Bonnard.V@wanadoo.fr> wrote in message
> > news:382705BA.A02@wanadoo.fr...
> > [Dave Abraham's code]
> > > > struct Int { int x; }
> > > > vector<Int> v(20);
> > >

> > He doesn't want undefined behavior. It's certainly about defined
behavior.
> > The initial values of the integers are undefined, not the behavior.

> Yes the behavior is undefined.  The initialization will initalized the
> items in the vector with a default initialized struct Int.  Since the
> member x doesn't get initialized in the code below the lvalue to
> rvalue conversion produces undefined behavior. (see 4.1 / 1) The code
> above is OK however.

That's the quote I was looking for.  However, it seems stronger than
what I was looking for -- it doesn't seem to make an exception for char
and unsigned char, which means that formally, the following program
invokes undefined behavior:

    struct S
    {
        char            c[ 100 ] ;
    } ;

    S               s1 ;
    strcpy( s1.c , "x" ) ;
    S               s2 ;
    unsigned char*  dst = (unsigned char*)(void*)(&s2) ;
    unsigned char*  src = (unsigned char*)(void*)(&s1) ;
    for ( int i = 0 ; i < sizeof( S ) ; ++ i ) {
        dst[ i ] = src[ i ] ;
    }

This is rather a pain, because it is (under various variants) a commun
idiom in C.

--
James Kanze                    mailto:James.Kanze@dresdner-bank.com
Conseils en informatique orient   e objet/
                  Beratung in objekt orientierter Datenverarbeitung
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