• Simon (38/38) Mar 23 2019 Hi,
• kinke (7/9) Mar 23 2019 The problem is that the C++ compiler uses head-const for the
• Simon (2/11) Mar 23 2019 I didn't know specifying the mangle was possible, thanks!

Simon <simon.vanbernem yahoo.de> writes:

Hi,
I experienced some trouble with DMD today, while trying to 
declare an external C++ function in D, that gets linked from a 
C++ compiled object file.

The C++ function that I want to link against is declared as 
follows:
bool ColorEdit4(const char* label, float col[4], int flags = 0);

Yielding the following signature in the .obj (using a demangler):
BOOL __cdecl ImGui::ColorEdit4(char const * __ptr64,float * 
__ptr64 const,int)

The Function is declared in D as follows:
extern(C++, ImGui) bool ColorEdit4(const(char)* label, float[4] 
col, int flags = 0);

Which unfortunately crashes the compiler, which tells me I can't 
use a D array-type here, and should use a pointer. If you want to 
know the full story, you can look into the bug-report: 
https://issues.dlang.org/show_bug.cgi?id=19759

So as a workaround until this is fixed, I somehow need to end up 
with the same mangled function signature, while using a pointer 
type for the second argument.

I tried:
extern(C++, ImGui) bool ColorEdit4(const(char)* label, const 
float* col, int flags = 0);

which yields:
BOOL __cdecl ImGui::ColorEdit4(char const * __ptr64,float * 
__ptr64,int)

so the 2nd argument is of type "float * __ptr64", when it should 
be "float * __ptr64 const".

Trying "const float* col" or "const(float)* col" doesn't yield 
the correct result either ("float const * __ptr64 const" and 
"float const * __ptr64"), and I didn't find any other 
combinations I could try.

Is there any way to end up with the correct mangled function 
signature, using only pointer types? Another workaround would of 
course be to switch to C-Linkage, so the names don't get mangled 
at all, but the C++-object file has function overloads, so I 
would like to avoid that. If this isn't possible, I might just 
wait for the dmd update.

kinke <noone nowhere.com> writes:

On Saturday, 23 March 2019 at 11:35:45 UTC, Simon wrote:
 Is there any way to end up with the correct mangled function 
 signature, using only pointer types?

The problem is that the C++ compiler uses head-const for the 
array param (`float * const`), which cannot be represented in D.
What you can do is specify the mangle manually, e.g.:

pragma(mangle, "?ColorEdit4 ImGui  YA_NPEBDQEAMH Z")
extern(C++) bool ColorEdit4(const(char)* label, float* col, int 
flags = 0);

Simon <simon.vanbernem yahoo.de> writes:

On Saturday, 23 March 2019 at 13:04:10 UTC, kinke wrote:
 On Saturday, 23 March 2019 at 11:35:45 UTC, Simon wrote:
 Is there any way to end up with the correct mangled function 
 signature, using only pointer types?

 The problem is that the C++ compiler uses head-const for the 
 array param (`float * const`), which cannot be represented in D.
 What you can do is specify the mangle manually, e.g.:

 pragma(mangle, "?ColorEdit4 ImGui  YA_NPEBDQEAMH Z")
 extern(C++) bool ColorEdit4(const(char)* label, float* col, int 
 flags = 0);

I didn't know specifying the mangle was possible, thanks!