如何将对象从D传递给C++？

Question

我正在尝试与C++和D进行互操作.而我今天发现的东西真的让我大吃一惊:对象没有在我的程序中正确传递.

最好是展示一个例子.

我有一个C++库,我编译成一个目标文件和D程序,我与我的库链接并运行.

他们来了:

#include <stdio.h>

class Color
{
public:
  Color(unsigned int _r, unsigned int _g, unsigned int _b) : r(_r), g(_g), b(_b) {}

  unsigned int r, g, b;
};

class Printer
{
public:
  Printer() {}
  ~Printer() {}
  static Printer* getInstance();
  void print(Color *c);
};

Printer* Printer::getInstance()
{
  return new Printer();
}

void Printer::print(Color *c)
{
  printf("(%d, %d, %d)\n", c->r, c->g, c->b);
}

和D程序:

import std.stdio;

extern(C++)
{
  class Color
  {
    uint r, g, b;

    this(uint _r, uint _g, uint _b)
    {
      r = _r;
      g = _g;
      b = _b;
    }
  }

  class Printer
  {
    @disable this();
    static Printer getInstance();
    final void print(Color c);
  }
}

void main()
{
  auto printer = Printer.getInstance();

  Color c = new Color(42, 7, 19);

  printer.print(c);
}

我用这些命令编译它们:

c++ -c my_core.cpp -o my_core.o
dmd main.d my_core.o -L-lstdc++

但是当我跑步时./main,我得到了奇怪的结果:

(113244372, 1, 42)

是什么让我认为对象被错误传递只是一个简单的实验.首先,我运行了几次我的程序,这就是我所看到的:

$ ./main
(266442332, 1, 42)
$ ./main
(234899036, 1, 42)
$ ./main
(109475420, 1, 42)

所以第一个数字似乎是一个指向内存块的指针.我对装配知识的第六种感觉让我觉得它是this变量的指针.

现在,只是为了确认我的数据仍然存在且这些数字不仅仅是随机的,我还在我的课程中添加了两个字段Color:

C++ lib:

#include <stdio.h>

class Color
{
public:
  Color(unsigned int _r, unsigned int _g, unsigned int _b, unsigned int _u, unsigned int _v) : r(_r), g(_g), b(_b), u(_u), v(_v) {}

  unsigned int r, g, b, u, v;
};

class Printer
{
public:
  Printer() {}
  ~Printer() {}
  static Printer* getInstance();
  void print(Color *c);
};

Printer* Printer::getInstance()
{
  return new Printer();
}

void Printer::print(Color *c)
{
  printf("(%d, %d, %d, %d, %d)\n", c->r, c->g, c->b, c->u, c->v);
}

和D程序:

import std.stdio;

extern(C++)
{
  class Color
  {
    this(uint _r, uint _g, uint _b, uint _u, uint _v)
    {
      r = _r;
      g = _g;
      b = _b;
      u = _u;
      v = _v;
    }

    uint r, g, b, u, v;
  }

  class Printer
  {
    @disable this();
    static Printer getInstance();
    final void print(Color c);
  }
}

void main()
{
  auto printer = Printer.getInstance();

  Color c = new Color(42, 7, 19, 499, 727);

  printer.print(c);
}

产出是:

$ ./main                         
(90379876, 1, 42, 7, 19)
$ ./main
(79758948, 1, 42, 7, 19)
$ ./main
(74901092, 1, 42, 7, 19)
$ ./main
(217458276, 1, 42, 7, 19)
$ ./main
(238933604, 1, 42, 7, 19)

我尝试用DMD和LDC编译器编译我的程序,但两者都为我提供了完全相同的行为.

UPD:更有趣的是(可能)指出问题所在,是在C++ lib中创建的事实对象正在D和C++之间正确传递.

为了证明这一点,我在Color班上创建了"工厂方法" :

static Color* create(unsigned int _r, unsigned int _g, unsigned int _b, unsigned int _u, unsigned int _v) {
    return new Color(_r, _g, _b, _u, _v);
}

然后,在D程序中:

Color c = Color.create(42, 7, 19, 499, 727);

printer.print(c);

这样c对象来自C++库,被传递给printer对象,在C++库中创建,这个传输是在D程序中完成的.

结果出人意料地正确:

$ ./main
(42, 7, 19, 499, 727)

我是否错过了C++和D interop的概念,或者这是两个D编译器中的错误(令人怀疑)？

Answer 1

您不应该使用 Ds new 来分配 C++ 类，如果您创建 Color::getInstance 它就可以工作。

import std.stdio;

extern(C++)
{
  class Color
  {
    this(uint _r, uint _g, uint _b, uint _u, uint _v)
    {
      r = _r;
      g = _g;
      b = _b;
      u = _u;
      v = _v;
    }

    uint r, g, b, u, v;
    static Color getInstance(uint _r, uint _g, uint _b, uint _u, uint _v);
  }

  class Printer
  {
    @disable this();
    static Printer getInstance();
    final void print(Color c);
  }
}

void main()
{
  auto printer = Printer.getInstance();
  auto c = Color.getInstance(42, 7, 19, 499, 727);

  printer.print(c);
}

和

#include <stdio.h>

class Color
{
public:
  Color(unsigned int _r, unsigned int _g, unsigned int _b, unsigned int _u, unsigned int _v) : r(_r), g(_g), b(_b), u(_u), v(_v) {}

  unsigned int r, g, b, u, v;
  static Color* getInstance (unsigned int _r, unsigned int _g, unsigned int _b, unsigned int _u, unsigned int _v);
};

Color* Color::getInstance(unsigned int _r, unsigned int _g, unsigned int _b, unsigned int _u, unsigned int _v)
{
  return new Color(_r, _g, _b, _u, _v);
}

class Printer
{
public:
  Printer() {}
  ~Printer() {}
  static Printer* getInstance();
  void print(Color *c);
};

Printer* Printer::getInstance()
{
  return new Printer();
}

void Printer::print(Color *c)
{
  printf("(%d, %d, %d, %d, %d)\n", c->r, c->g, c->b, c->u, c->v);
}