c++ - 如何为在 C 中使用 C++ 代码创建包装器？

Question

我正在尝试为 C++ 第三方库做一个 C 包装器，因为我需要在我的 C 项目中使用它。我看过 C++ 类包装器的示例，但我不了解该过程，也无法包装 C++ 结构。

我要包装的结构:

struct confGlobal{
    long int device;
    string name;
    int number;
    string uid;
    string message;
    bool mode;

    confiGlobal():device{LONG_MAX}, number{INT_MAX}{}
};

struct product{
    string id;
    string name;
};
struct category{
    unsigned char id;
    string name;
    string description;

    category():id{UCHAR_MAX}{}
};
struct subCategory{
    unsigned char id;
    string name;
    string description;
    unsigned char idRoot;

    subCategory():id{UCHAR_MAX}, idRoot{UCHAR_MAX}{}
};
struct confPartner{
    vector<struct product> tableProduct;
    vector<struct category> tableCategory;
    vector<struct subCategory> tableSubCategory;
};

调用此方法:

class my_API {
public:
    static my_API* Instance(struct confGlobal cGlobal,
                        struct confPartner cPartner);
   ... another methods ...
private:
    virtual ~my_API();
    struct confGlobal cGlobal;
    struct confPertner cPartner;
};

我需要填充此结构并从 C 调用 my_API::Instance()，但我的尝试没有成功。

包装器.h

#ifdef __cplusplus
extern "C" {
#endif
struct confGlobal_wpr; // An opaque type that we'll use as a handle
typedef struct confGlobal_wpr confGlobal_wpr;
confGlobal_wpr *confGlobal_create(unsigned int device,
                     char *name,
                     int number,
                     char *uid,
                     char *message,
                     unsigned char mode);

struct product_wpr{
    char id[4];
    char name[30];
};
typedef struct product_wpr product_wpr;

struct category_wpr{
    unsigned char id;
    char name[3];
    char description[30];
};
typedef struct category_wpr category_wpr;

struct subcategory_wpr{
    unsigned char id;
    char name[3];
    char description[30];
    unsigned char idRoot;
};
typedef struct subCategory_wpr subCategory_wpr;
struct confPartner_wpr; // An opaque type that we'll use as a handle
typedef struct confPartner_wpr confPartner_wpr;
confPartner_wpr *confPartner_create(Product_wpr tableProducts[],
                     unsigned char numProducts,
                     Category_wpr tableCategories[],
                     unsigned char numCategories,
                     SubCategory_wpr tableSubCategories[],
                     unsigned char numSubCategories);

struct my_api_wpr;
typedef struct my_api_wpr my_api_wpr;

my_api_wpr *my_api_create(struct confGlobal_wpr cGlobal,
                     struct confPartner_wpr cPartner);

#ifdef __cplusplus
}
#endif

包装器.cpp

confGlobal_wpr *confGlobal_create(unsigned int device,
                     char *name,
                     int number,
                     char *uid,
                     char *message,
                     unsigned char mode)
{
    confGlobal_wpr *cg;
    struct confGlobal confiGlobal;
    confiGlobal.name = name;
    confiGlobal.device = device;
    confiGlobal.number = number;
    confiGlobal.uid = uid;
    confiGlobal.message = message;
    if (mode == 0)
        confiGlobal.mode = false;
    else
        confiGlobal.mode = true;
    return cg;
}
void confGlobal_destroy(confGlobal_wpr *cg)
{
    if (cg == NULL)
        return;
    delete static_cast<confGlobal_wpr *>(cg->instance); // ERROR: invalid static_cast from type ‘confGlobal’ to type ‘confGlobal_wpr*’
    free(cg);
}

confPartner_wpr *confPartner_create(product_wpr tableProducts_wpr[],
                     unsigned char numProducts,
                     category_wpr tableCategories_wpr[],
                     unsigned char numCategories,
                     subCategory_wpr tableSubCategories_wpr[], 
                     unsigned char numSubCategories)
{
    unsigned char i=0;

    confPartner_wpr *cc;
    struct confPartner cPartner;
    vector< struct product> tableProduct;
    vector< struct category> tableCategory;
    vector< struct subCategory> tableSubCategory;

    for (i=0; i<numProducts; i++)
    {
        struct product p;
        p.id = tableProducts_wpr[i].id;
        p.name = tableProducts_wpr[i].name;
        tableProduct.push_back(p);
    }
    cPartner.tableProduct = tableProducts;

    for (i=0; i<numCategories; i++)
    {       
        struct category c;
        c.id = tableCategories_wpr[i].id;
        c.nombre = tableCategories_wpr[i].name;
        c.descripcion = tableCategories_wpr[i].description;
        tableCategory.push_back(c);
    }
    cPartner.tableCategory = tableCategory;

    for (i=0; i<numSubCategories; i++)
    {
        struct subZona sc;
        sc.id = tableSubCategories_wpr[i].id;
        sc.name = tableSubCategories_wpr[i].name;
        sc.description = tableSubCategories_wpr[i].description;
        sc.idRoot = tableSubCategories_wpr[i].idRoot;
        tableSubCategory.push_back(sc);     
    }
    cPartner.tableSubCategory = tableSubCategory;
    return cc;

}

my_api_wpr *my_api_create(struct confGlobal_wpr confiGlobal_wpr,
                      struct confPartner_wpr confiPartner_wpr)
{
    my_api_wpr *my_api;
    my_API *obj;
    my_api = (typeof(my_api))malloc(sizeof(*my_api));
    obj    = my_API::Instance(confiGlobal_wpr, confiConsorcio_wpr);
    /* With this compile and linked OK
    confGlobal cg;
    confPartner cc;
    obj    = my_API::Instance(cg, cc);
    */
    my_api->obj = obj;

    return my_api;
}
void my_api_destroy(ct_api_wpr *my_api)
{
    if (my_api == NULL)
        return;
    delete static_cast<my_API *>(my_api->ptr_api); // ERROR: ‘virtual my_API::~my_API()’ is private within this context
    free(my_api);
}

编译链接时的输出错误:

g++ -shared -o libwrapper.so *.cpp wrapper.h -l:libthird-party.a -L. -ldl -lrt -Wl,-rpath /usr/local/lib -lc

In function ‘my_api_wpr* my_api_create(confGlobal_wpr, confPartner_wpr)’:
error: no matching function for call to ‘my_API::Instance(confGlobal_wpr&, confPartner_wpr&)’
  obj    = my_API::Instance(confiGlobal_wpr, confiConsorcio_wpr);
                                                               ^
my_API.h:30:20: note: candidate: static my_API* my_API::Instance(confGlobal, confPartner)
     static my_API* Instance(struct confGlobal cGlobal, struct confiPartner cPartner);
                    ^~~~~~~~
my_API.h:30:20: note:   no known conversion for argument 1 from ‘confGlobal_wpr’ to ‘confGlobal’

Answer 1

您忘记了 CT_API::Instance 不理解您在 C 中创建的用于包装 C++ 结构的“句柄”类型。如果您阅读错误消息，这正是它告诉您的内容。您必须将它们转换回适当的 C++ 类型。

首先，由于您正在使用“创建”样式的例程来构建结构并将它们作为指针返回，因此您应该考虑让您的 my_api_create 函数接受指针。特别是因为生成的句柄类型是前向声明的结构，在 C 中没有可见的定义，您的 C 客户端不可能取消引用它们。

这突出了另一个问题。您也没有在 C++ 中正确使用这些句柄。

所以，一次做一件事......

您在 C 中的创建例程应声明为:

my_api_wpr *my_api_create(struct confGlobal_wpr* cGlobal, struct confPartner_wpr* cPartner);

在 C++ 方面，您需要实际定义您的句柄类型。像这样的东西:

extern "C" struct confGlobal_wpr {
    struct confGlobal instance;
};

extern "C" struct confPartner_wpr {
    struct confPartner instance;
};

extern "C" struct my_api_wpr {
    my_API *ptr;
};

现在，你的创作:

confGlobal_wpr *confGlobal_create(unsigned int device,
                                  char *name,
                                  int number,
                                  char *uid,
                                  char *message,
                                  unsigned char mode)
{
    confGlobal_wpr *cg = new confGlobal_wpr;
    struct confGlobal& cGlobal = cg->instance; //<-- note the reference
    // TODO: populate cGlobal as usual
    return cg;
}

confPartner_wpr *confPartner_create(product_wpr tableProducts_wpr[],
                                    unsigned char numProducts,
                                    category_wpr tableCategories_wpr[],
                                    unsigned char numCategories,
                                    subCategory_wpr tableSubCategories_wpr[],
                                    unsigned char numSubCategories)
{
    confPartner_wpr *cc = new confPartner_wpr;
    struct confPartner& cPartner = cc->instance; //<-- note the reference
    // TODO: populate cPartner as usual
    return cc;
}

my_api_wpr *my_api_create(struct confGlobal_wpr* cGlobal, struct confPartner_wpr* cPartner)
{
    my_api_wpr *my_api = new my_api_wpr;
    my_api->ptr = CT_API::Instance(cGlobal->instance, cPartner->instance);
    return my_api;
}

您还应该为上述所有内容添加相应的 _destroy 方法。