在C ++中导出类及其派生数据成员

问题描述

您好。我需要在C ++中导出一个我写过的类。它不是一个子类，因此它不必与其超类一起导出，但它具有从各种DLL派生的数据成员和函数，如setupapi.dll，user32.dll，MPUSBAPI.dll。我是否也需要出口它们？如果是这样，怎么样？在此先感谢。

Hi. I need to export a class in C++ dll i''ve written. It isn''t a subclass so it doesn''t have to be exported along with its superclasses but it has data members and functions derived from various DLL such as setupapi.dll, user32.dll, MPUSBAPI.dll. Do i need to export them too or not? If so, how? Thanks in advance.

推荐答案

class /*__declspec( dllexport/dllimport )*/ MY_API CMyClass
{
//...
};

并导出该类的实例

and exporting an instance of the class

extern MY_API CMyClass AnInstance;

首先允许客户端代码创建自己的CMyClass实例，第二个用于查看DLL在模块范围内提供的单个实例。

如果有疑问，请使用第一种技术。

另一件事：导出的类中没有任何公共数据成员。使用访问器函数获取，设置。它更便携，更安全，特别是当DLL可以拥有自己的堆并进行自己的内存管理时。

The first allows the client code to create its own instance of CMyClass, the second to see a single instance provided at module scope by the DLL.
If in doubt use the first technique.
One other thing: Don''t have any public data members in the exported class. Use accessor functions Get, Set. It''s more portable and safer that way especially when DLLs can have their own heaps and do their own memory management.

#ifndef __MYHEADER_H__
#define __MYHEADER_H__

#pragma pack(push,8)

class MyClass
{
  char b;
  long long ll;
  bool b2;
public:


  inline char getb() const { return b; }
  inline long long getll() const { return ll; }
};

#pragma pack(pop)

如果客户端代码使用不同的对齐方式而不是使用#pragma pack编译的代码，则确保内存对齐保持不变正如预期的那样。



祝你好运

Espen Harlinn

If client code uses a different alignment than your code was compiled with #pragma pack ensures that memory alignment stays as expected for your code.

Best regards
Espen Harlinn

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