Re: Static intialization of flexible arrays in C++

[Nitin Karkhanis <nkarkhan at yahoo dot com>]

Thank you for your email.

Flexible arrays are indeed legal. 
http://gcc.gnu.org/onlinedocs/gcc-3.4.3/gcc/Zero-Length.html#Zero-Length
(and it really is not a hack or a bad trick :), it has
been used for ages and I would be hard-pressed to come
up with an equally elegant solution to represent
variable size arrays )
The trick of using the max array size is not workable
in embedded applications where memory is at a premium.
And then there is the static intialization problem.

e.g
typedef struct {

} a_t;

I thought C++ is a superset of C and C code should
compile in a C++ compiler (except for strict type
checking) ..but guess not.

N.

--- Eljay Love-Jensen <eljay@adobe.com> wrote:

> Hi Nitin,
> 
>  >Static initializations of a flexible array works
> with gcc but not with 
> g++ . is this by design?
> 
> Yes, this is by design.  C++ does not have flexible
> arrays (or what I've 
> heard called "stretchy arrays" or "stretchy
> buffers").  C++ has STL 
> std::vector.
> 
> The stretchy buffer is a bad trick -- it's not
> portable, and may cause 
> certain optimizations to fail is a bad way.
> 
> (I'm not sure if it is even legit C code.  Maybe it
> is with C99.  I dunno.)
> 
> A suggestion is to do the reverse:  specify the
> structure with the array 
> given the maximum length, and allow allocations of
> less-than-maximum when 
> used off the heap.  (There are caveats with this
> approach as well.)
> 
> struct flex_array_1000
> {
>    int A;
>    int Data[1000];
> };
> 
> Alternatively, you can use template structs to
> provide more exacting 
> "hard-coded" arrays.
> 
> template <int Count>
> struct flex_array
> {
>    int A;
>    int Data[Count];
> };
> 
> ...and you can have the struct derived from a common
> base class if you need 
> some sort of polymorphism.
> 
> HTH,
> --Eljay 
> 
> 



		
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