DLL文件中的多个类 [英] Multiple Classes in DLL file

问题描述

我在这里遇到的问题几乎是一个愚蠢的问题，但我只是无法在网络上找到答案。
当我想创建一个DLL项目（不在一个现有的c ++项目中）时，我读到我需要在.h文件的开头实现以下几行：

what I've got here is pretty much a dumb and noobie question, but I just can`t find an answer on the web. When I want to create a DLL project (out of an existing c++ project), I read that I need to implement the following lines in the beginning of the .h files:

#ifdef _EXPORTING
#define CLASS_DECLSPEC    __declspec(dllexport)
#else
#define CLASS_DECLSPEC    __declspec(dllimport)
#endif

我看了MSDN中的示例：

I looked at the example in the MSDN:

// MathFuncsDll.h
#ifdef MATHFUNCSDLL_EXPORTS
#define MATHFUNCSDLL_API __declspec(dllexport) 
#else
#define MATHFUNCSDLL_API __declspec(dllimport) 
#endif

现在我想了解一下，是否需要更改我进行的每个新课程的 _EXPORTING和 CLASS_DECLSPEC？
例如，如果要在与 MathFuncsDll.h相同的项目中创建一个名为 foo的类，则需要将以下行放在.h文件的开头：

Now I want to understand, do I need to change the "_EXPORTING" and the "CLASS_DECLSPEC" for every new class I make? For example if I'd create a class named "foo" within the same project as "MathFuncsDll.h" I'd need to put the following lines at the start of the .h file:

// FooDll.h
#ifdef FOO_EXPORTS
#define FOO_API __declspec(dllexport) 
#else
#define FOO_API __declspec(dllimport) 
#endif

在项目的所有.h文件中都一样？

Or is some line is the same in all .h files of the project?

还有另一件事，如果我使用命名空间来引用整个dll作为一个文件并从中提取类，是否需要在每个.h文件中将使用命名空间* NAME * 放入？

And another thing, if I use a namespace to reference the whole dll as one and extract the classes from it, do I need to put the using namespace *NAME* in every .h file?

推荐答案

不，您不必为每个类创建新的宏：

No, you need not to create new macros for each classes:

class MATHFUNCSDLL_API Foo {...};
class MATHFUNCSDLL_API Boo {...};
class MATHFUNCSDLL_API MyNewClass {...};

第二个问：不要在头文件中使用命名空间：使用名称空间在c ++标题中

For the second q: don't use using namespace inside header file: "using namespace" in c++ headers

您的标题可能如下所示：

Your header can looks like the following:

#pragma once
namespace foo {
    class MATHFUNCSDLL_API Foo {...};
    class MATHFUNCSDLL_API Boo {...};
    class MATHFUNCSDLL_API MyNewClass {...};
}

已编辑

// mylibdef.h
#pragma once
#ifdef _EXPORTING
#define CLASS_DECLSPEC    __declspec(dllexport)
#else
#define CLASS_DECLSPEC    __declspec(dllimport)
#endif

// myclass1.h
#pragma once
#include "mylibdef.h"
namespace mylib {
class CLASS_DECLSPEC MyClass1 {...};   
}

// myclass2.h
#pragma once
#include "mylibdef.h"
namespace mylib {
class CLASS_DECLSPEC MyClass2 {...};   
}

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