From:	"Elias Pschernig" <f DOT x DOT gruber-museum-arnsdorf AT magnet DOT at>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: What's the idea with ALLEGRO.H's zero-size arrays?
Date:	Mon, 1 Nov 1999 22:06:03 +0100
Organization:	Telenor magnet GmbH
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To:	djgpp AT delorie DOT com
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>Hi!
>
>I tried to compile my new program with '-pedantic' switch, but
>djgpp shows me following data....
>
>djgpp/include/allegro.h:948: warning: ANSI C++ forbids zero-size
array `line'
>djgpp/include/allegro.h:1498: warning: ANSI C++ forbids zero-size
array `dat'
>
>What's the idea with zero-size arrays?

They are used in structures with changeable size.
If you have

struct bitmap {
  int w,h...
  void *line[0]; // zero size array
};

,you can allocate a bitmap with x lines later with

a_bitmap=...malloc(sizeof(struct bitmap)+sizeof(void *)*x);

.Now the array has x elements really.

The idea is that you have only one call to malloc. Without the zero
size array, you'd have to store a pointer in the bitmap structure, and
do a second malloc to create the list of line pointers...


Elias Pschernig

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