C structs

[Johann Lermer via Digitalmars-d-learn]

Hi,

I'm fiddling around with cairo (downloaded 
fromhttps://github.com/D-Programming-Deimos/cairo) and I stumbled 
over this problem:

(file rectandmatrix.d)
----
import deimos.cairo.cairo;

void main ()
{
     cairo_rectangle_int_t rect;
     cairo_matrix_t matrix;
}
----

Compiling that with 'dmd rectandmatrix' fails with this error:

rectandmatrix.o: In function `_Dmain':
rectandmatrix.d:(.text._Dmain+0x18): undefined reference to 
`_D6deimos5cairo5cairo14cairo_matrix_t6__initZ'
collect2: error: ld returned 1 exit status
--- errorlevel 1

The rectangle is OK - no error there. The matrix however, 
produces the error. The difference between both is that 
cairo_rectangle_int_t is a struct containing integers, and 
cairo_matrix_t contains doubles.

I can, however, compile like that:

'dmd rectandmatrix deimos/cairo/cairo.d' (deimos being in a 
subdir of the working directory)

then cairo.d is compiled as well and linked to the code.

So, my questions are:

1) Why do I have to compile and link cairo.d - it's only an 
definition file for C code and IMHO there shouldn't be any need 
to compile cairo.d at all.

2) Why ist a struct containing only integers handled so 
differently from a struct holding doubles?

Thanks