How to pass a null pointer to a C function

[Craig Dillabaugh]

On Sunday, 1 December 2013 at 04:11:57 UTC, Simen Kjærås wrote:
> On 2013-12-01 04:46, Craig Dillabaugh wrote:
>> Since questions about calling C from D seem to be popular 
>> today, I
>> thought I would throw this one out there.
>>
>> I am trying to call a C function which takes as parameters 
>> several
>> arrays of doubles.  It is valid to have some arrays passed a 
>> NULL
>> pointers in the C code.
>> To call this from D I've come up with the following, but it 
>> seems like a
>> bit of a hack.
>>
>> double[] x1 = [ 2.4, 3.7, 9.7, 4.5 ];
>> double[] y1 = [ 2.4, 9.8, 9.1, 3.4 ];
>> double[] empty;
>>
>> SHPObject*[] shape_ptrs;
>> shape_ptrs ~= SHPCreateSimpleObject( SHPT_POLYGON, 
>> to!int(x1.length),
>>                        x1.ptr, y1.ptr, empty.ptr );
>>
>> It should be clear what is going on.  A POLYGON is defined as 
>> a set of
>> points (provided as arrays of doubles), with X,Y and optional Z
>> coordinates.
>> In this case I want a 2D polygon, so I want the final Z array 
>> to be
>> empty.
>>
>> I wanted to just write 0 as the final parameter, but that 
>> didn't work, so
>> I tried to!(double*)(0), and that didn't make the compiler 
>> happy either.
>>
>> I guess using the empty.ptr bit makes sense, in that the final 
>> array is
>> meant to be empty, so pass it a pointer to an empty array.  
>> But it seems
>> a bit hackish that I need to declare an additional empty array 
>> just to
>> call this function.
>>
>> Is there an accepted 'proper' way of passing NULL pointers to C
>> functions from D?
>
> Well, there is null.
>
> --
>   Simen

Simen and Mike. Thanks!

Now I feel stupid.