如何使用智能指针围绕 C“对象"实现包装器? [英] How to implement a wrapper around C 'objects' using smart pointers?

问题描述

我正在使用一个 C 库，它使用来自 C++ 的原始指针.因此，我正在考虑将所有指向 C 对象的指针包装在 C++ 类中并将它们转换为智能指针.我已经建立了一个工作示例:

I am using a C library which uses raw pointers from C++. Therefore, I'm looking into wrapping all the pointers to C objects in C++ classes and turning them into smart pointers. I've built a working example:

#include <iostream>
using namespace std;

// the C library is oop: using structs and naming conventions. Like this: 

// C library declarations
struct Animal_s {
    int age;
};
typedef struct Animal_s Animal;

Animal* make_animal(int age);

void free_animal(Animal* animal);

Animal* do_something_with_animal(Animal* animal);



// C lib implementations
Animal* make_animal(int age ){
    auto* animal = (Animal*) malloc(sizeof(Animal));
    animal->age = age;
    return animal;
}

void free_animal(Animal *animal){
    free(animal);
}

Animal* do_something_with_animal(Animal* animal){
    //...
    return animal;
}



// C++ wrapper 
class AnimalWrapper{
    Animal* animal_; // how to use smart pointers? 

public:
    explicit AnimalWrapper(int age){
        animal_ = make_animal(age);
    };

    ~AnimalWrapper(){
        free_animal(animal_);
    }

    AnimalWrapper(const AnimalWrapper& animalWrapper){
        if (this != &animalWrapper){
            animal_ = animalWrapper.animal_;
        }
    }

    AnimalWrapper(AnimalWrapper&& animalWrapper) noexcept {
        if (this != &animalWrapper){
            animal_ = animalWrapper.animal_;
        }
    }
    AnimalWrapper& operator=(const AnimalWrapper& animalWrapper)  {
        if (this != &animalWrapper){
            animal_ = animalWrapper.animal_;
        }
        return *this;
    }

    AnimalWrapper& operator=(AnimalWrapper&& animalWrapper) noexcept {
        if (this != &animalWrapper){
            animal_ = animalWrapper.animal_;
        }
        return *this;
    }

    Animal *getAnimal() const {
        return animal_;
    }

    Animal* doSomethingWithAnimal(){
        return do_something_with_animal(animal_);
    }
};



int main(){

    AnimalWrapper animalWrapper(6);


    return 0;
};

这个例子有效，根据 valgrind，正确管理内存.但是，是否可以使用智能指针实现包装类?或者我必须手动管理包装类中的内存?

This example works and according to valgrind, mangages the memory correctly. However, is it possible to implement the wrapper class using smart pointers? Or must I manually manage the memory in the wrapper classes?

推荐答案

您可以使用 std::unique_ptr 用于管理 Animal 对象的生命周期:

You can use std::unique_ptr for managing lifetime of Animal objects:

#include <memory>

struct FreeAnimal {
    void operator()(Animal* a) const noexcept {
        free_animal(a);
    }
};

using AnimalPtr = std::unique_ptr<Animal, FreeAnimal>;

int main() {
    AnimalPtr party_animal{make_animal(21)};

    do_something_with_animal(&*party_animal);
    // or
    do_something_with_animal(party_animal.get());
}

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