包装用于C消耗的C ++类API [英] Wrapping C++ class API for C consumption

问题描述

我有一组相关的C ++类，它们必须从DLL中打包和导出，以便C / FFI库可以轻松使用。我正在寻找一些最佳做法这样做。例如，如何创建和释放对象，如何处理基类，替代解决方案等...

I have a set of related C++ classes which must be wrapped and exported from a DLL in such a way that it can be easily consumed by C / FFI libraries. I'm looking for some "best practices" for doing this. For example, how to create and free objects, how to handle base classes, alternative solutions, etc...

我迄今为止的一些基本指导是将方法转换为简单函数带有表示this指针的额外void *参数，包括任何析构函数。构造函数可以保留其原始参数列表，但必须返回一个表示该对象的指针。所有内存都应该通过同一组进程范围的分配和自由例程来处理，并且在某种意义上应该通过宏或其他方式进行热插拔。

Some basic guidelines I have so far is to convert methods into simple functions with an extra void* argument representing the 'this' pointer, including any destructors. Constructors can retain their original argument list, but must return a pointer representing the object. All memory should be handled via the same set of process-wide allocation and free routines, and should be hot-swappable in a sense, either via macros or otherwise.

任何建议。

推荐答案

Foreach的公共方法你需要一个C函数。

你还需要一个不透明的指针在C代码中表示你的类。

只要使用一个void *就更简单，虽然你可以创建一个包含void *和其他信息的结构体（例如，如果你想支持数组？） 。

Foreach public method you need a C function.
You also need an opaque pointer to represent your class in the C code.
It is simpler to just use a void* though you could build a struct that contains a void* and other information (For example if you wanted to support arrays?).

Fred.h
--------------------------------

#ifdef  __cplusplus
class Fred
{
    public:
    Fred(int x,int y);
    int doStuff(int p);
};
#endif

//
// C Interface.
typedef void*   CFred;

//
// Need an explicit constructor and destructor.
extern "C" CFred  newCFred(int x,int y);
extern "C" void   delCFred(CFred);

//
// Each public method. Takes an opaque reference to the object
// that was returned from the above constructor plus the methods parameters.
extern "C" int    doStuffCFred(CFred,int p);

实现是微不足道的。

将opaque指针转换为Fred然后调用该方法。

The the implementation is trivial.
Convert the opaque pointer to a Fred and then call the method.

CFred.cpp
--------------------------------

// Functions implemented in a cpp file.
// But note that they were declared above as extern "C" this gives them
// C linkage and thus are available from a C lib.
CFred newCFred(int x,int y)
{
    return reinterpret_cast<void*>(new Fred(x,y));
}

void delCFred(CFred fred)
{
    delete reinterpret_cast<Fred*>(fred);
}

int doStuffCFred(CFred fred,int p)
{
    return reinterpret_cast<Fred*>(fred)->doStuff(p);
}

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