如何将非静态成员函数作为unique_ptr删除器传递 [英] How to pass a non-static member function as a unique_ptr deleter

问题描述

#include <memory>
#include <iostream>
#include <exception>
#include <curl/curl.h>

class client
{
private:
    std::unique_ptr<CURL, decltype(&psclient::del_curl)> uptr_curl_;

    inline CURL * init_curl()
    {
        CURLcode result = curl_global_init(CURL_GLOBAL_DEFAULT);
        if(result != CURLE_OK)
            throw std::logic_error(curl_easy_strerror(result));
        return curl_easy_init();
    }

    inline void del_curl(CURL * ptr_curl)
    {
        curl_easy_cleanup(ptr_curl);
        curl_global_cleanup();
    }
public:
    inline client()
    : uptr_curl_(init_curl(), &client::del_curl)
    {
    }
}

编译器保持抱怨没有匹配的构造函数用于'std： ：unique_ptr< CURL，void（*）（CURL *）>'

看起来像声明是正确的删除模板参数。它是一个函数指针，返回void，并以CURL *作为参数。这符合 del_curl 的签名。

It seems to me like the declaration is correct for the deleter template argument. It is a function pointer that returns void and takes a CURL * as an argument. This matches the signature of del_curl.

在C ++中还有另一个随机规则，对非静态成员函数指针的模板参数的要求？如果是，为什么？

Is there yet another random rule, unknown to me, in C++ that specifies a requirement for template arguments to non-static member function pointers? If so, why?

推荐答案

@R的答案。 Sahu是正确的imo。但是，如果你坚持传递非静态成员函数deleter，这里是一个使用好旧的 std :: bind 和 std :: function ：

The answer of @R. Sahu is correct imo. However, if you insist of passing a non-static member function deleter, here is a way of doing it using the good old std::bind and std::function:

#include <memory>
#include <iostream>
#include <functional>

class Foo
{
private:
    std::unique_ptr<int, std::function<void(int*)>> _up;
public:
    Foo(): _up(new int[42], std::bind(&Foo::deleter, this, std::placeholders::_1))
    {

    }
    void deleter(int* p)
    {
        delete[] p;
        std::cout << "In deleter" << std::endl;
    }
};

int main()
{
    Foo foo;
}

PS：我只是不喜欢 bind

PS: I just don't like the bind, I wonder if one can improve on that.

使用lambda：

Foo(): _up(new int[42],
               [this](int* p)->void
               {
                   deleter(p);
               }
          ){}

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