Passing static array to C variadic function
Daniel Gibson via Digitalmars-d
digitalmars-d at puremagic.com
Sun Jul 20 09:00:41 PDT 2014
Hi,
I have a C variadic function (passed from C code into my D code via
function pointer) that I need to call with a static array.
So according to the D documentation, static arrays are passed by value
in D2 and by reference in C and D1.
(Even though http://dlang.org/abi.html claims "Static arrays are passed
as pointers to their first element." - I guess this just wasn't updated
for D2)
For "normal" functions http://dlang.org/interfaceToC.html tells me to
add a "ref" in the function signature, to tell D to pass it by reference
(couldn't this be implicit for extern (C) functions?) - But I obviously
can't to this for vararg function arguments.
So let's imagine the following code:
extern (C) alias funPtr_t = ptrdiff_t function( ptrdiff_t arg, ... );
funPtr_t fun = ...; // is assigned somewhere..
void bla( float[3] v ) {
fun( 42, v );
}
This produces the following compiler error (DMD 2.065 linux amd64):
"Error: cannot pass static arrays to extern(C) vararg functions"
/However/, if I typedef a float[3] type, the compiler does not complain
(not sure if the code behaves like expected, though, or if it's still
passed by value instead of by reference as expected by the C code):
typedef float[3] vec3_t;
void bla( vec3_t v ) {
fun( 42, v );
}
Then again, if I use alias instead of the deprecated typedef:
alias vec3_t = float[3];
I again get "Error: cannot pass static arrays to extern(C) vararg
functions".
Is there a "proper" way to make this work?
If not, any ideas for a viable workaround?
Cheers,
Daniel
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