C callbacks getting a value of 0! Bug in D?

[Johnson Jones via Digitalmars-d-learn]

On Monday, 28 August 2017 at 21:35:27 UTC, Steven Schveighoffer 
wrote:
> On 8/27/17 10:17 PM, Johnson Jones wrote:
>> [...]
>
> For C/C++ interaction, always use c_... types if they are 
> available. The idea is both that they will be correctly defined 
> for the width, and also it will mangle correctly for C++ 
> compilers (yes, long and int are mangled differently even when 
> they are the same thing).
>
> -Steve

and where are these c_ types defined? The reason I replaced them 
was precisely because D was not finding them.