struct inititalization in C and in C++

struct inititalization in C and in C++

Edgar Reynaldo

Major Reynaldo

May 2007

Hey, I have this code which won't compile. The first half I guess would work in C, but it does not work in C++. The second way almost works, but the order of the parameters is wrong and since ALLEGRO_VERTEX is an opaque structure it might change, and I don't know the correct order anyway.

/*
   ALLEGRO_VERTEX quad[4] = {// counterclockwise from top left
      {.x = viewdrawx             , .y = viewdrawy              , .z = 0.0 , .color = white , .u = texlx , .v = texty},
      {.x = viewdrawx             , .y = viewdrawy + viewheight , .z = 0.0 , .color = white , .u = texlx , .v = texby},
      {.x = viewdrawx + viewwidth , .y = viewdrawy + viewheight , .z = 0.0 , .color = white , .u = texrx , .v = texby},
      {.x = viewdrawx + viewwidth , .y = viewdrawy              , .z = 0.0 , .color = white , .u = texrx , .v = texty}
   };
//*/
   ALLEGRO_VERTEX quad[4] = {// counterclockwise from top left
      {viewdrawx             , viewdrawy              , 0.0 , {white} , texlx , texty},
      {viewdrawx             , viewdrawy + viewheight , 0.0 , {white} , texlx , texby},
      {viewdrawx + viewwidth , viewdrawy + viewheight , 0.0 , {white} , texrx , texby},
      {viewdrawx + viewwidth , viewdrawy              , 0.0 , {white} , texrx , texty}
   };

What's the best way to initialize an opaque C struct in C++?

Edit
I like this option :

Quote:

Option D:

FooBar FooBarMake(int foo, float bar)

Legal C, legal C++. Easily optimizable for PODs. Of course there are no named arguments, but this is like all C++. If you want named arguments, Objective C should be better choice.

Eagle and Allegro 5 binaries | Older Allegro 4 and 5 binaries | Allegro 5 compile guide
King Piccolo will make it so Then I could just flip it with some sweet, sweet matrix math. In either case, I’ll ride this wagon until the wheels fall off. Thanks to those that keep it running

SiegeLord

Member #7,827

October 2006

ALLEGRO_VERTEX is not opaque.

This should be ok: {x, y, z, u, v, color}.

"For in much wisdom is much grief: and he that increases knowledge increases sorrow."-Ecclesiastes 1:18
[SiegeLord's Abode][Codes]:[DAllegro5]:[RustAllegro]

bamccaig

Member #7,536

July 2006

As for opaque types, IMO there needs to be a public API, or else you aren't supposed to touch it. You should never directly access an opaque structure. Your only access to it should be through the API.

--
I mean the best with what I say. It doesn't always sound that way.

Edgar Reynaldo

Major Reynaldo

May 2007

SiegeLord said:

ALLEGRO_VERTEX is not opaque.

How do you know when a struct is opaque?

Quote:

This should be ok: {x, y, z, u, v, color}.

The manual documents them in the order x, y, z, color, u, v. It's kind of misleading.

Arthur Kalliokoski

Second in Command

February 2005

Edgar Reynaldo said:

How do you know when a struct is opaque?

If it were truly opaque, there'd be no include file available to user programs to say what the members were. Some interfaces aren't really opaque, such as stdio, but if you don't treat them as such you're in for a lot of pain.

They all watch too much MSNBC... they get ideas.

Thomas Fjellstrom

Member #476

June 2000

Allegro has some opaque types. the header only declares:

struct ALLEGRO_FOO;

so you can't access anything inside it. An internal header will define the structure for allegro internal code.

--
Thomas Fjellstrom - [website] - [email] - [Allegro Wiki] - [Allegro TODO]
"If you can't think of a better solution, don't try to make a better solution." -- weapon_S
"The less evidence we have for what we believe is certain, the more violently we defend beliefs against those who don't agree" -- https://twitter.com/neiltyson/status/592870205409353730

SiegeLord

Member #7,827

October 2006

Edgar Reynaldo said:

How do you know when a struct is opaque?

If this code compiles: Struct a; then Struct is not opaque.

Quote:

The manual documents them in the order x, y, z, color, u, v. It's kind of misleading.

This has now been fixed.

"For in much wisdom is much grief: and he that increases knowledge increases sorrow."-Ecclesiastes 1:18
[SiegeLord's Abode][Codes]:[DAllegro5]:[RustAllegro]

Edgar Reynaldo

Major Reynaldo

May 2007

Thanks for fixing the docs.