如何使用 C++ 静态类方法创建 C 风格的回调

大多数示例没有清楚地显示如何使用静态类方法创建 std::function，该方法将对象实例作为第一个参数。

我想采用一个静态类方法，该方法将对象实例作为第一个参数，并创建一个可以用作 C 样式回调函数并可以访问对象实例的新函数。

我似乎什么都试过了。我在这里拿了这个例子，并试图通过在这里使用一个类似的例子将它重构到我的用例中，但没有运气。

请参阅下面的更多最新示例

#include <functional>
#include <iostream>

struct Foo
{
    Foo(int me) : m_me(me) {}

    static int foo_static(Foo* f, int a, int b) { return f->m_me + a + b; }
    int m_me;
};

int main()
{
    Foo f(4);

    using std::placeholders::_1;
    std::function<int(int,int)> new_func = std::bind(&Foo::foo_static, &f, _1);

    std::cout << new_func(3, 4) << std::endl;
}

编辑

忘记编译器输出

$ c++ main.cpp -std=c++14
main.cpp:25:30: error: no viable conversion from '__bind<int (*)(Foo *, int, int), Foo *, const std::__1::placeholders::__ph<1> &>' to
      'std::function<int (int, int)>'
        std::function<int(int,int)> new_funct = std::bind(&Foo::foo_static, &f, _1);
                                    ^           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/functional:1627:5: note: candidate constructor not
      viable: no known conversion from '__bind<int (*)(Foo *, int, int), Foo *, const std::__1::placeholders::__ph<1> &>' to 'std::nullptr_t'
      (aka 'nullptr_t') for 1st argument
    function(nullptr_t) _NOEXCEPT : __f_(0) {}
    ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/functional:1628:5: note: candidate constructor not
      viable: no known conversion from '__bind<int (*)(Foo *, int, int), Foo *, const std::__1::placeholders::__ph<1> &>' to
      'const std::__1::function<int (int, int)> &' for 1st argument
    function(const function&);
    ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/functional:1629:5: note: candidate constructor not
      viable: no known conversion from '__bind<int (*)(Foo *, int, int), Foo *, const std::__1::placeholders::__ph<1> &>' to
      'std::__1::function<int (int, int)> &&' for 1st argument
    function(function&&) _NOEXCEPT;
    ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/functional:1631:5: note: candidate template
      ignored: requirement '__callable<__bind<int (*)(Foo *, int, int), Foo *, const __ph<1> &> >::value' was not satisfied [with _Fp =
      std::__1::__bind<int (*)(Foo *, int, int), Foo *, const std::__1::placeholders::__ph<1> &>]
    function(_Fp);
    ^
1 error generated.

这里有更多关于我要完成的任务的详细信息。m_callback 是我想要设置的。我可以将回调中需要的内容推送到 ClientData 中，但我喜欢 Command 结构来保存它的数据，而不必创建一个新结构作为每个命令的 ClientData 传递。

#include <functional>
#include <iostream>
#include <string>

typedef void (* callback) (Client* client, ClientData* client_data);

struct Command
{
    int execute() = 0;
}

struct Search : Command
{
    enum SearchType { kType1, kType2 };

    Search(Logger log, std::string query, SearchType type) : m_log(log), m_callback(), m_query(query), m_typ(type)
    {
        m_callback = // create callback
    }

    int execute(Client* client, ClientData* client_data)
    {
        client->query(client_data, m_callback, m_query, m_type);
    }

    static int my_callback(Foo* f, Client* client, ClientData* client_data);

    Logger& m_log;
    callback m_callback;
    std::string m_query;
    SearchType m_type;
    // other data I want in the callback that isn't passed in client_data
};

int main()
{
    Logger log;
    Search search(log, "some search", Search::kType1);
    Client client;
    ClientData client_data;

    search.execute(&client, client_data);
}

所以我想出了我做错了什么，std::bind但现在我需要将它转换为我需要使用的 C 样式回调。