c++ api 转 c api

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Jul 2, 2021

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Translating a C++ API to a C API requires creating a "wrapper" around the C++ class(es) to allow them to be utilized by C code. Here's a step-by-step guide to help you perform this translation:

Flatten the class hierarchy: C does not support classes, so you'll need to flatten the class hierarchy by converting member functions to regular functions that take a pointer to a structure representing the object as the first argument.

Create a C-compatible structure: As C doesn't support namespaces, class inheritance, or access specifiers like public, private, and protected, you need to create a C-compatible structure that holds the data.

Example

C++ class:


class MyClass {
public:
    MyClass();
    ~MyClass();
    int MyFunction(int x);
private:
    int _value;
};

C-compatible structure:


typedef struct {
    int _value;
} MyClass;

Create C wrapper functions: Create wrapper functions for constructors, destructors, and member functions. You'll need to provide a C-compatible name for the functions, and you'll have to manage the memory yourself using malloc() and free().

Example

C wrapper functions:


extern "C" {
    // Constructor
    MyClass* MyClass_create();

    // Destructor
    void MyClass_destroy(MyClass* my_class);

    // Member function
    int MyClass_MyFunction(MyClass* my_class, int x);
}

Implement C wrapper functions: Now implement these wrapper functions in C++.

Example

C++ implementation:


#include "MyClass.h"

extern "C" {
    MyClass* MyClass_create() {
        return new MyClass();
    }

    void MyClass_destroy(MyClass* my_class) {
        delete my_class;
    }

    int MyClass_MyFunction(MyClass* my_class, int x) {
        return my_class->MyFunction(x);
    }
}

Expose the C API: Expose the C API's header file (.h) to C applications, and compile your C++ code as a shared library (.dll, .so, or .dylib).

Now you can use your C++ API from C by including the header file and linking against the shared library.

Remember to always account for best practices and error handling, as this example is a simplified illustration of the process.

如果您的 C++ 类使用了标准库的 vector 类型，则需要使用 C 兼容的数组来替换它。

下面是一个示例：


#include <vector>

class MyClass {
public:
    MyClass();
    ~MyClass();
    void MyFunction(std::vector<int>& vec);
private:
    int _value;
};

为了将 MyClass 转换为 C 兼容的结构体，您需要使用 C 兼容的数组来替换 vector 类型。例如，您可以使用一个包含指向整数的指针和数组大小的结构体。


typedef struct {
    int* data;
    int size;
} IntArray;

typedef struct {
    IntArray vec;
    int _value;
} MyClass;

extern "C" {
    MyClass* MyClass_create();
    void MyClass_destroy(MyClass* my_class);
    void MyClass_MyFunction(MyClass* my_class, IntArray vec);
}

MyClass* MyClass_create() {
    return new MyClass();
}

void MyClass_destroy(MyClass* my_class) {
    delete[] my_class->vec.data;
    delete my_class;
}

void MyClass_MyFunction(MyClass* my_class, IntArray vec) {
    for (int i = 0; i < vec.size; i++) {
        // Process vec.data[i]
    }
}

在这个例子中，我们使用了一个 IntArray 结构体来代替 vector 类型。我们还定义了 MyClass 和 IntArray 的包装函数和实现。

当您需要处理标准库的 vector 类型时，这个过程可能会变得更加复杂。但是，您可以使用类似的方法将 vector 替换为 C 兼容的数组。