No matching function to call: error: must use ‘.’ or ‘->’ to call pointer-to-member function in ‘f (...)’, e.g. ‘(... ->* f) (...)’

Question

我正在尝试从线程池调用非静态成员函数。提交函数告诉我错误：必须使用‘.’或‘->’来调用‘f(...)’中的指向成员函数的指针，例如第一行的 std::future* f) (...)”。我试图不创建静态函数。我尝试了几种组合，但我认为我不明白它的要求。有人愿意帮忙吗？

auto submit(F&& f, Args&&... args) -> std::future<decltype(f(args...))> {
        // Create a function with bounded parameters ready to execute
        std::function<decltype(f(args...))()> func = std::bind(std::forward<F>(f), std::forward<Args>(args)...);
        // Encapsulate it into a shared ptr in order to be able to copy construct / assign 
        auto task_ptr = std::make_shared<std::packaged_task<decltype(f(args...))()>>(func);

        // Wrap packaged task into void function
        std::function<void()> wrapper_func = [task_ptr]() 
        {
            (*task_ptr)(); 
        };

        // Enqueue generic wrapper function
        m_queue.enqueue(wrapper_func);

        // Wake up one thread if its waiting
        m_conditional_lock.notify_one();

        // Return future from promise
        return task_ptr->get_future();
    }

Compiler Output

更新：我changed auto submit(F&& f, Args&&... args) -> std::future<decltype(f(args...))>到auto submit(F&& f, Args&&... args) -> std::future<std::invoke_result_t<F, Args...>>

现在我收到一个新的编译器错误“没有名为 'type' 的类型”。下图。

no type named 'type' compiler error

Answer 1

要正确获取调用成员函数或普通函数的结果类型，您必须使用 std::invoke_result_t:

auto submit(F&& f, Args&&... args) -> std::future<std::invoke_result_t<F, Args...>> {
    // ...
}

这样，成员函数和非成员函数都可以工作。

考虑发送成员函数时，必须同时传递实例：

// object of type MyClass -----v
submit(&MyClass::member_func, my_class, param1, param2);

No matching function to call: error: must use ‘.’ or ‘->’ to call pointer-to-member function in ‘f (...)’, e.g. ‘(... ->* f) (...)’

No matching function to call: error: must use ‘.’ or ‘->’ to call pointer-to-member function in ‘f (...)’, e.g. ‘(... ->* f) (...)’

c++

syntax

g++

function

No matching function to call: error: must use ‘.*’ or ‘->*’ to call pointer-to-member function in ‘f (...)’, e.g. ‘(... ->* f) (...)’

No matching function to call: error: must use ‘.*’ or ‘->*’ to call pointer-to-member function in ‘f (...)’, e.g. ‘(... ->* f) (...)’

c++

syntax

g++

function

No matching function to call: error: must use ‘.’ or ‘->’ to call pointer-to-member function in ‘f (...)’, e.g. ‘(... ->* f) (...)’

No matching function to call: error: must use ‘.’ or ‘->’ to call pointer-to-member function in ‘f (...)’, e.g. ‘(... ->* f) (...)’