Re: [boost] Access to unaligned (packed) structs

From: Roland Schwarz (roland.schwarz_at_[hidden])
Date: 2007-10-11 03:30:05

Zara wrote:
> class foo {
>   private:
>     unsigned char internals[5];
>   public:
>     char a() {return internals[0];}
>     int b() {
>       // select code block depending on your endianness
>       unsigned int n=(a[0]<<24)|(a[1]<<16]|(a[2]<<8)|a[3];
>       unsigned int n=(a[3]<<24)|(a[2]<<16]|(a[1]<<8)|a[0];
>       return static_cast<int>(n);
>     }
> };

Thank you for the answer, but the solution is only close to what I 
requested.

Access syntax in your solution is:

data.a()

while I want

data.a

I.e. a has to be an object on its own that has a type conversion 
operator for the access.

My problem as far as I can currently see, boils down to another question:

I have

struct bar
{
}

and

struct foo
{
     bar a;
}

How can I give bar access to its "container"?

Perhaps like so:

struct foo
{
     foo() {
         a.setref(this);
     }
     bar a;
}

But this implies runtime cost, which I want to avoid.

Another solution:

struct foo
{
     foo() : a(this) {}

     bar a;
}

While I am not sure if this avoids the runtime cost, I am also unsure if
this is valid C++ at all. At least the microsoft compiler spills out a 
warning.

Roland aka speedsnail