问c++11线程类如何使用类成员函数
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Stack Overflow用户

提问于 2014-01-11 14:05:29

回答 4查看 18.9K关注 0票数 19

我的程序如下所示

#include <iostream>
#include <thread>

class A {
public:
    void foo(int n ) { std::cout << n << std::endl; }
};

int main()
{
    A a;

    std::thread t1(&A::foo, std::ref(a), 100);

    t1.join();
    return 0;
}

当我使用下面的命令编译它时，我得到了错误

g++ -o main main.cc -lpthread -std=c++11

错误：

In file included from /usr/local/include/c++/4.8.2/thread:39:0,
                  from check.cc:2:
/usr/local/include/c++/4.8.2/functional: In instantiation of ‘struct std::_Bind_simple<std::_Mem_fn<void (A::*)(int)>(std::reference_wrapper<A>, int)>’:
/usr/local/include/c++/4.8.2/thread:137:47:   required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (A::*)(int); _Args = {std::reference_wrapper<A>, int}]’
check.cc:13:42:   required from here
/usr/local/include/c++/4.8.2/functional:1697:61: error：no type named ‘type’ in ‘class std::result_of<std::_Mem_fn<void (A::*)(int)>(std::reference_wrapper<A>, int)>’
        typedef typename result_of<_Callable(_Args...)>::type result_type;
                                                              ^
/usr/local/include/c++/4.8.2/functional:1727:9: error：no type named ‘type’ in ‘class std::result_of<std::_Mem_fn<void (A::*)(int)>(std::reference_wrapper<A>, int)>’
          _M_invoke(_Index_tuple<_Indices...>)
          ^

c++

c++11

回答 4

Stack Overflow用户

回答已采纳

发布于 2014-01-11 14:08:22

这里不是引用包装器的正确位置。然而，一个简单的指针就足够了，并达到了预期的结果：

std::thread t1(&A::foo, &a, 100);

票数 24

Stack Overflow用户

发布于 2014-01-21 00:37:34

关于你的问题标题，我会使用lambda来构造线程。通过调用成员函数或绑定参数，使用或不使用引用。

 std::thread t1([&] { a.foo(100); });

票数 10

Stack Overflow用户

发布于 2015-10-03 09:08:29

好的，问题是ref(obj)返回一个对象的引用(别名)，而不是一个指针(地址)！要使用线程，我们需要指针，而不是引用！下面是一个将函数指针与线程一起使用的方便程序：

    #include <iostream>
    #include "vector"
    #include "string"
    #include "thread"
    #include "atomic"
    #include "functional"

    #include "stdlib.h"
    #include "stdio.h"
    #include "string.h"
    #include "assert.h"

    using namespace std;
    //__________________________Global variables_________________________________________________

    atomic<int> var(0);

    //__________________________class____________________________________________________________

    class C
    {
    public:

        C()
        {}

        static void addition (int a, int b)
        {
            for(int i= 0; i< a+b; i++)
                var++;
        }

        void subtraction (int a, int b)
        {
            for(int i= 0; i< a+b; i++)
                var--;
        }
    };

    class D : std::atomic<int>
    {
    public:
        D() : std::atomic<int>(0)
        {}

        void increase_member (int n)
        {
            for (int i=0; i<n; ++i)
                fetch_add(1);
        }

        int get_atomic_val()
        {
            return this->load();
        }
    };

    //________________________________functions________________________________________________

    void non_member_add (int a, int b)
    {
        for(int i= 0; i< a+b; i++)
            var++;
    }

    //__________________________________main____________________________________________________

    int main ()
    {
        int a=1, b=5;

    // (I)...........................................static public member function (with no inheritance).........................................

        void (* add_member_func_ptr)(int,int) = C::addition;            // pointer to a static public member function

        //defining thread pool for ststic public member_add_ptr

        vector<thread> thread_pool;

        for (int i=0; i<5; i++)
        {
            thread_pool.push_back(thread(add_member_func_ptr,a,b));
        }

        for(thread& thr: thread_pool)
            thr.join();

        cout<<"static public member function (with no inheritance)\t"<<var<<endl;

        //defining thread pool for ststic public member function

        var=0;

        thread_pool.clear();

        for (int i=0; i<5; i++)
        {
            thread_pool.push_back(thread(C::addition,a,b));             //void (* add_member_func_ptr)(int,int) is equal to C::addition
        }

        for(thread& thr: thread_pool)
            thr.join();

        cout<<"static public member function (with no inheritance)\t"<<var<<endl;

    // (II)..............................................non-static public member function (with no inheritance)...................................

        C bar;

        void (C::* sub_member_func_ptr)(int,int) = & C::subtraction;            // pointer to a non-static public member function

        var=0;

        //defining thread pool for non-ststic public member function

        thread_pool.clear();

        for (int i=0; i<5; i++)
        {
            thread_pool.push_back(thread(sub_member_func_ptr,bar,a,b));
        }

        for(thread& thr: thread_pool)
            thr.join();

        cout<<"non-static public member function (with no inheritance)\t"<<var<<endl;

        var=0;

        //defining thread pool for non-ststic public member function

        thread_pool.clear();

        for (int i=0; i<5; i++)
        {
            thread_pool.push_back(thread(&C::subtraction,bar,a,b));         //void (C::* sub_member_func_ptr)(int,int) equals & C::subtraction;
        }

        for(thread& thr: thread_pool)
            thr.join();

        cout<<"non-static public member function (with no inheritance)\t"<<var<<endl;


    // (III)................................................non-member function .................................................

        void (* non_member_add_ptr)(int,int) = non_member_add;              //pointer to a non-member function

        var=0;

        //defining thread pool for non_member_add

        thread_pool.clear();

        for (int i=0; i<5; i++)
        {
            thread_pool.push_back(thread(non_member_add,a,b));
        }

        for(thread& thr: thread_pool)
            thr.join();

        cout<<"non-member function\t"<<var<<endl<<endl;

    // (IV)...........................................non-static public member function (with inheritance).........................

        D foo;

        void (D::* member_func_ptr) (int) = & D::increase_member;                  //pointer to a non-static public member function of a derived class

        //defining thread pool for non-ststic public member function of a derived class

        thread_pool.clear();

        for (int i=0; i<5; i++)
        {
            thread_pool.push_back(thread(member_func_ptr,&foo,10));                 //use &foo because this is derived class!
        }

        for(thread& thr: thread_pool)
            thr.join();

        cout<<"non-static public member function (with inheritance)\t"<<foo.get_atomic_val()<<endl;

        //defining thread pool for non-ststic public member function

        D poo;

        thread_pool.clear();

        for (int i=0; i<5; i++)
        {
            reference_wrapper<D> poo_ref= ref(poo);

            D& poo_ref_= poo_ref.get();             //ref(obj) returns a reference (alias) to an object not a pointer(address)!

            D* d_ptr= &poo;                         //to work with thread we need pointers not references!


            thread_pool.push_back(thread(&D::increase_member, d_ptr,10));             //void (D::* member_func_ptr) (int) equals & D::increase_member;
        }

        for(thread& thr: thread_pool)
            thr.join();

        cout<<"non-static public member function (with inheritance)\t"<<poo.get_atomic_val()<<endl<<endl;


        return 0;
    }

票数 0

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/21059115

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