1. 给std::unique_ptr定制删除器

1.1 方法一，使用functor

#include <iostream>
#include <memory>
#include <stdio.h>

struct FileCloser{
    void operator()(FILE* fp) const{
        fclose(fp);
        fp = nullptr;

        std::cout << "file automatically closed.\n";
    }
};

auto main()->int {
    std::unique_ptr<FILE, FileCloser> pfile(fopen("1.txt", "w"));
}

1.2 方法二，使用函数指针

#include <iostream>
#include <memory>
#include <stdio.h>

auto main()->int{
    // 删除器可修改，但指针大小增长一倍
    std::unique_ptr<FILE, void(*)(FILE*)> pfile(fopen("2.txt", "w"), [](FILE* pf){fclose(pf); pf = nullptr; std::cout << "file automatically closed.\n";});
}

1.3 方法三，使用未求值的lambda

#include <iostream>
#include <memory>
#include <stdio.h>

auto main()->int{
    // 未求值的lambda，g++ main.cpp -std=c++20
    // 适合单次使用，不适合做接口，因为lambda表达式在每次使用都属于不同的类型
    std::unique_ptr<FILE, decltype([](FILE* fp){fclose(fp); fp = nullptr; std::cout << "file auto closed.\n";})> pfile(fopen("3.txt", "w"));
}
}

2. 给std::shared_ptr定制删除器

2.1 方法一

#include <iostream>
#include <memory>
#include <stdio.h>

struct FileCloser{
    void operator()(FILE* fp) const{
        fclose(fp);
        fp = nullptr;

        std::cout << "file automatically closed.\n";
    }
};

auto main()->int {
    std::shared_ptr<FILE> pfile(fopen("1.txt", "w"), FileCloser());
}

2.2 方法二

#include <iostream>
#include <memory>
#include <stdio.h>

auto main()->int{
    std::shared_ptr<FILE> pfile(fopen("2.txt", "w"), [](FILE* pf){fclose(pf); pf = nullptr; std::cout << "file automatically closed.\n";});
}

2.3 方法三

#include <iostream>
#include <memory>
#include <stdio.h>

auto main()->int{
    std::shared_ptr<FILE> pfile(fopen("3.txt", "w"), [](FILE* fp){
        if(fp){fclose(fp); fp = nullptr;} std::cout << "file auto closed.\n";});
}