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Re: Allocating memory styles

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On 07/20/2015 02:36 PM, janus wrote:
> Hello All,
> 
> 
> I am going through a book and I stumbled on this class of memory
> allocation:
> 
> void* p = calloc(1, class->size);
> 
> *(const struct Class**) P = class;
> 
> The last line is what is hard for me to understand. Why casting to
> pointer-to-pointer, and then dereference it immediately?  My
> understanding is that struct Class is the first element in P struct,
> so by casting P struct by struct class, one immediately has access to
> the first element of the struct. This makes sense to me. But why
> using pointer-to-pointer?
> 
> I was thinking that the same thing might be achieved by this:
> 
> (const struct Class*) P = class; Regards, \Emeka
> 
can you show the whole snippet? I think something is missing...
There are special ways of initializing structs(I believe libfreetype uses such)...

might be related to this...

> error = FT_New_Face( library, "/usr/share/fonts/truetype/arial.ttf", 
> 0, &face );

They have face be a pointer type, then &face is a pointer to a pointer.
So they can set *face=NULL inside the function, if stuff goes wrong. Would not work by-value.
(It would 'work' as face=NULL, but not visible outside). 

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Allocating memory styles janus <emekamicro@gmail.com> - 2015-07-20 05:36 -0700
  Re: Allocating memory styles Noob <root@127.0.0.1> - 2015-07-20 14:53 +0200
    Re: Allocating memory styles janus <emekamicro@gmail.com> - 2015-07-20 07:23 -0700
      Re: Allocating memory styles Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-20 16:40 +0100
        Re: Allocating memory styles janus <emekamicro@gmail.com> - 2015-07-20 12:19 -0700
  Re: Allocating memory styles Richard Heathfield <rjh@cpax.org.uk> - 2015-07-20 14:07 +0100
  Re: Allocating memory styles Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-20 14:18 +0100
  Re: Allocating memory styles jt@toerring.de (Jens Thoms Toerring) - 2015-07-20 13:47 +0000
    Re: Allocating memory styles Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-20 15:21 +0100
  Re: Allocating memory styles Johann Klammer <klammerj@NOSPAM.a1.net> - 2015-07-20 16:27 +0200
  Re: Allocating memory styles luser droog <luser.droog@gmail.com> - 2015-07-20 12:34 -0700
    Re: Allocating memory styles Keith Thompson <kst-u@mib.org> - 2015-07-20 14:00 -0700
      Re: Allocating memory styles luser droog <luser.droog@gmail.com> - 2015-07-20 20:29 -0700
        Re: Allocating memory styles raltbos@xs4all.nl (Richard Bos) - 2015-07-22 15:21 +0000
    Re: Allocating memory styles janus <emekamicro@gmail.com> - 2015-07-20 14:13 -0700
  Re: Allocating memory styles "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-07-20 14:54 -0700
    Re: Allocating memory styles "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-07-20 14:57 -0700

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