Re: Ada Smileys in C++ lib Conversion

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 16 Sie, 14:30, Brian Drummond <brian_drumm...@btconnect.com> wrote:

> The real case was a bit stranger than previous reply (simplifying to a 1-D
> array)
>
> const int xdim = 7;    
> const int size = xdim;  // was a function of all dimensions
> int array[size];
> ...
> error: initializer element is not constant
> error: variably modifed 'array' at file scope
>
> So a "const" is not constant, says the compiler.

The above is guaranteed to work by the C++ standard (nerds see
5.19/1).

The problem will be when the initializer for "size" above will indeed
be a function call - this would not be a constant expression, even
though the object "size" is declared as const.
The reason is that constant expression should always evaluate to the
same value, whereas function calls are not required (and cannot be
verified) to do so.

So, there is a difference between a "constant expression" (roughly
equivalent to Ada's "static expression") and a "const object".
Array bounds require constant expression.

--
Maciej Sobczak * http://www.inspirel.com

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