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digitalmars.D.learn - How to call a extern C++ class constructor ?

reply Luhrel <lucien.perregaux gmail.com> writes:
Hello there,

I would like to know how can I call a C++ ctor.

Actually, I have this:

C++:
CppClass.cpp
----------------
#include "CppClass.h"


AmazingCppClass::AmazingCppClass()
{
	number = 124;
}

int AmazingCppClass::getNumber(bool show)
{
	if (show)
		printf("Number: %s", number);
	return number;
}

void AmazingCppClass::add(int num)
{
	number += num;
}
----------------
CppClass.h:
----------------
#include <stdio.h>


class AmazingCppClass
{
private:
	int number;

public:
	AmazingCppClass();
	int getNumber(bool show);
	void add(int num);
};
----------------

D:
app.d
----------------
import std.stdio;

void main()
{
	auto dcpp = new AmazingCppClass();
	dcpp.getNumber(true); //segfault here
}

extern(C++) class AmazingCppClass
{
	this();

	int getNumber(bool show);

	void add(int num);
}
----------------

But somehow I got a segfault on dcpp.getNumber(true).
I found that there's a __cpp_new 
(https://dlang.org/phobos/core_stdcpp_new_.html), but I have no 
idea how to use it and the doc doesn't say a lot about this 
(https://dlang.org/spec/cpp_interface.html#using_cpp_classes_from_d)

Do you guys know ?
Feb 01 2020
next sibling parent reply Ferhat =?UTF-8?B?S3VydHVsbXXFnw==?= <aferust gmail.com> writes:
On Saturday, 1 February 2020 at 08:15:20 UTC, Luhrel wrote:

 Hello there,

 I would like to know how can I call a C++ ctor.

 [...]


You cannot. 
https://dlang.org/spec/cpp_interface.html#using_cpp_classes_from_d

You must use a factory method like createInstance.
Feb 01 2020
parent reply Luhrel <lucien.perregaux gmail.com> writes:
On Saturday, 1 February 2020 at 08:21:29 UTC, Ferhat Kurtulmuş 
wrote:

 You cannot. 
 https://dlang.org/spec/cpp_interface.html#using_cpp_classes_from_d

 You must use a factory method like createInstance.


Oh I see, so there's definitively no way to call a c++ ctor 
without modifying the c++ code ?
Feb 01 2020
parent reply Ferhat =?UTF-8?B?S3VydHVsbXXFnw==?= <aferust gmail.com> writes:
On Saturday, 1 February 2020 at 08:27:07 UTC, Luhrel wrote:

 On Saturday, 1 February 2020 at 08:21:29 UTC, Ferhat Kurtulmuş 
 wrote:

 You cannot. 
 https://dlang.org/spec/cpp_interface.html#using_cpp_classes_from_d

 You must use a factory method like createInstance.


 Oh I see, so there's definitively no way to call a c++ ctor 
 without modifying the c++ code ?


İf you are not allowed to modify that c++ code, you can write a 
createInstance function in your custom cpp file.
Feb 01 2020
parent reply Luhrel <lucien.perregaux gmail.com> writes:
On Saturday, 1 February 2020 at 08:32:51 UTC, Ferhat Kurtulmuş 
wrote:

 On Saturday, 1 February 2020 at 08:27:07 UTC, Luhrel wrote:

 On Saturday, 1 February 2020 at 08:21:29 UTC, Ferhat Kurtulmuş 
 wrote:

 You cannot. 
 https://dlang.org/spec/cpp_interface.html#using_cpp_classes_from_d

 You must use a factory method like createInstance.


 Oh I see, so there's definitively no way to call a c++ ctor 
 without modifying the c++ code ?


 İf you are not allowed to modify that c++ code, you can write a 
 createInstance function in your custom cpp file.


That was my fear.
Feb 01 2020
parent reply norm <norm.rowtree gmail.com> writes:
On Saturday, 1 February 2020 at 08:38:22 UTC, Luhrel wrote:

 On Saturday, 1 February 2020 at 08:32:51 UTC, Ferhat Kurtulmuş 
 wrote:

 On Saturday, 1 February 2020 at 08:27:07 UTC, Luhrel wrote:

 On Saturday, 1 February 2020 at 08:21:29 UTC, Ferhat 
 Kurtulmuş wrote:

 You cannot. 
 https://dlang.org/spec/cpp_interface.html#using_cpp_classes_from_d

 You must use a factory method like createInstance.


 Oh I see, so there's definitively no way to call a c++ ctor 
 without modifying the c++ code ?


 İf you are not allowed to modify that c++ code, you can write 
 a createInstance function in your custom cpp file.


 That was my fear.


It isn't too bad, you need a simple wedge written in C++ that 
returns an instance of any T you want. A simple template function 
usually works, or to make it more generic you can use a variadic 
template to handle N args, but I find variadic templates in C++ 
are still annoying to use.
Feb 01 2020
parent Ferhat =?UTF-8?B?S3VydHVsbXXFnw==?= <aferust gmail.com> writes:
On Saturday, 1 February 2020 at 10:21:54 UTC, norm wrote:

 On Saturday, 1 February 2020 at 08:38:22 UTC, Luhrel wrote:

 On Saturday, 1 February 2020 at 08:32:51 UTC, Ferhat Kurtulmuş 
 wrote:

 On Saturday, 1 February 2020 at 08:27:07 UTC, Luhrel wrote:

 On Saturday, 1 February 2020 at 08:21:29 UTC, Ferhat 
 Kurtulmuş wrote:

 [...]


 Oh I see, so there's definitively no way to call a c++ ctor 
 without modifying the c++ code ?


 İf you are not allowed to modify that c++ code, you can write 
 a createInstance function in your custom cpp file.


 That was my fear.


 It isn't too bad, you need a simple wedge written in C++ that 
 returns an instance of any T you want. A simple template 
 function usually works, or to make it more generic you can use 
 a variadic template to handle N args, but I find variadic 
 templates in C++ are still annoying to use.


And do not forget to write a void cppDestroy(T instance) function 
that runs delete instance in c++ so that you can call it from D 
code.

void cppDestroy(T instance)
Feb 01 2020
prev sibling parent reply kinke <noone nowhere.com> writes:
On Saturday, 1 February 2020 at 08:15:20 UTC, Luhrel wrote:

 But somehow I got a segfault on dcpp.getNumber(true).


That's because you declare it as virtual in D (default for 
classes, use `final`), but non-virtual in C++. You also forgot to 
add the class field to the D declaration (yes, D needs to know 
about the struct layout and size too, especially when you `new` 
the class in D and let the GC allocate it).

Trivial cases like yours should actually work wrt. using C++ ctor 
implementations from D IIRC.
Feb 01 2020
parent kinke <noone nowhere.com> writes:
On Saturday, 1 February 2020 at 14:52:21 UTC, kinke wrote:

 Trivial cases like yours should actually work wrt. using C++ 
 ctor implementations from D IIRC.


Ah, you need at least one virtual function in the C++ class 
(because D always reserves a vptr, the pointer to the class 
vtable).
Feb 01 2020