Re: [boost] Re: smart_ptr and handles

From: Jonathan Wakely (cow_at_[hidden])
Date: 2004-12-29 09:20:11

On Wed, Dec 29, 2004 at 02:51:27PM +0100, Dirk Gregorius wrote:

> Thanks for your help and sorry for not looking carefully at the 
> documentation:
> 
> I tried the following for a Windows device context:
> 
> The creation function is:     HDC GetDC( HWND)
> The deletion function is:     int ReleaseDC( HWND, HDC );
> 
> // Code like in the documentation...
> typedef  shared_ptr<void> handle;
> handle make_dc( HWND hWnd )
> {
>    // The release function takes two arguments, so I tried an adapter 
> functor...unfortunately it does not work
>    handle( GetDC( hWnd ), bind1( ReleaseDC, hWnd ) );
> }

Should that be bind, not bind1 ?

It's not hard to write your own deleter if you can't do it with a
binder:

    struct DCReleaser
    {
        DCReleaser(HWND hwnd) : hwnd(hwnd) {}
        void operator()(void* p) { ReleaseDC( hwnd, (HDC)p ); }
        HWND hwnd;
    };

    handle make_dc( HWND hWnd )
    {
       return handle( GetDC( hWnd ), DCReleaser(hWnd) );
    }

but ...

> My problem is to bind the window handle to the custom delete function. 
> My compilter spits aout a lot of  error messages here.
> Can I use boost::bind here or boost::function?

I think bind(ReleaseDC, hWnd, _1) should work.

> BTW: How does shared_ptr call the custom delete function? For a COM 
> object it should call in the D'tor:
> 
> raw_ptr->Release();
> 
> While in my case it should call ( what is the usual way in the C++  
> standard IIRC ):
> 
> Release( raw_ptr );
> 
> Does the shard_ptr interface figures this out in some clever way and 
> manage this internally?

The custom deleter's function operator is called with the managed
pointer as its argument, e.g. for a deleter d and pointer p: d(p)

jon

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 and behold, do ye now complain that ye lack freedom."
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