在D中使用C++类

Question

我试图找到一种在D中使用C++类的方法.

http://www.digitalmars.com/d/2.0/cpp_interface.html

D不能调用C++特殊成员函数,反之亦然.这些包括构造函数,析构函数,转换运算符,运算符重载和分配器.

所以,我试图将这些C++函数愚蠢地转换为C风格的函数调用.这是我正在使用的证据.

helper.h

class someClass {
    public:
        someClass();
        char *whatSayYou();
};

extern "C"
{
    someClass *hearMeOut();
}

helper.cpp

#include "helper.h"

someClass::someClass()
{

}

char *someClass::whatSayYou()
{
    return "Everything is gravy";
}


someClass *hearMeOut()
{
    return new someClass;
}

main.d

import std.stdio;

int main(string[] args)
{
    someClass *awesomeExample = hearMeOut();
    char *shoutoutToTheWorld = awesomeExample.whatSayYou();
    writefln(std.string.toString(shoutoutToTheWorld));
    return 0;
}


extern (C++)
{
    interface someClass
    {
        char *whatSayYou();
    }

    someClass *hearMeOut();
}

以下是我如何遵守它.

g++-4.3 -c -I code/dg3d_helper -I /usr/local/include/ -o code/dg3d_helper/helper.o code/dg3d_helper/helper.cpp
code/dg3d_helper/helper.cpp: In member function ‘char* someClass::whatSayYou()’:
code/dg3d_helper/helper.cpp:19: warning: deprecated conversion from string constant to ‘char*’
gdc-4.3 -g -c -I code/ -o code/main.o code/main.d
gdc-4.3 -g -I code/ -o main code/dg3d_helper/helper.o code/main.o -lstdc++

一旦调用该方法,我就会出现分段错误.

Program received signal SIGSEGV, Segmentation fault.
0x0000000000402fa0 in _Dmain (args=...) at code/main.d:7
7       char *shoutoutToTheWorld = awesomeExample.whatSayYou();
(gdb) bt
#0  0x0000000000402fa0 in _Dmain (args=...) at code/main.d:7
#1  0x000000000041b1aa in _D9dgccmain211_d_run_mainUiPPaPUAAaZiZi2goMFZv ()
#2  0x000000000041b235 in _d_run_main ()
#3  0x00002aaaab8cfc4d in __libc_start_main () from /lib/libc.so.6
#4  0x0000000000402d59 in _start ()

Answer 1

您的C++版本按值返回.

您的D版本希望它通过引用返回.

从本质上讲,您的C++版本在堆栈上粘贴了someClass的副本.D认为C++会将指针放在堆栈上.它试图将someClass的副本解释为指针,并发生不好的事情.

问题是在D中,类和接口总是通过引用返回.C++按值返回所有内容,除非您指明它是引用或指针.

因此你需要这个:

someClass * hearMeOut() { return new someClass; }

别忘了稍后删除它.

Answer 2

您还没有公开 C 接口。您的函数仍然返回 C++ 类，而不是 C 可以识别的内容。将您的类公开为void *s 。例如：

class MyClass
{
//private members
public:
//public members
    int MyMethod(int argument) const;
    virtual float MyVirtualMethod();
    virtual ~MyClass() {}
};

class MySecondClass : public MyClass
{
public:
    virtual float MyVirtualMethod();
    int MyMethod2(int argument) const;
};

extern "C" {
    void * CreateMyClass()
    {
        return static_cast<void *>(new(std::nothrow) MyClass);
    }

    void * CreateMySecondClass()
    {
        //Note the cast to the base class first (This is needed
        //because it might actually change the position of the pointer,
        //which would not be automatically adjusted later)
        return static_cast<void *>(static_cast<MyClass *>(new(std::nothrow) MySecondClass));
    }

    int CallMyClassMethod(void * thisMember, int argument)
    {
        return static_cast<MyClass *>(thisMember)->MyMethod(argument);
    }

    float CallMyVirtualMethod(void * thisMember)
    {
        return static_cast<MyClass *>(thisMember)->MyVirtualMethod();
    }

    int CallMyMethod2(void thisMember, int argument)
    {
        MyClass * convertedToMyClass = static_cast<MyClass *>(thisMember);
        MySecondClass * asSecondClass = dynamic_cast<MySecondClass *>(convertedToMyClass);
        if (!asSecondClass)
        {
            //Return error (thisMember not an instance of MySecondClass)
        }
        else
        {
            return asSecondClass->MyMethod2(argument);
        }
    }

    void DestroyMyClass(void * classMember)
    {
        delete static_cast<MyClass *>(classMember);
    }
}

这将使您的类可以由 D 使用，也可以由 C（以及与 C 绑定的所有其他语言）使用。