C++ 使用来自同一个类的函数在类内创建线程

Create thread inside class with function from same class

提问by user3728501

I want to be able to define a class with some data members, and a function which has access to those data members, which are to be private.

我希望能够定义一个包含一些数据成员的类，以及一个可以访问这些数据成员的函数，这些数据成员是私有的。

I then want a public function, which creates some threads, which operate on the data members of the class. I am having some trouble getting my code to compile.

然后我想要一个公共函数，它创建一些线程，这些线程对类的数据成员进行操作。我在编译代码时遇到了一些麻烦。

Don't worry about mutex or data protection, this isn't going to be a problem, since this is just some example code for testing.

不要担心互斥或数据保护，这不会成为问题，因为这只是一些用于测试的示例代码。

class foo {
    public:
    void make_foo_func_threads();

    private:
    void foo_func();

    char private_data;
    std::vector<std::thread> some_threads;
}

void foo::foo_func() {
    while(1) {
        private_data = 'A';
    }
}

void foo::make_foo_func_thread() {
    for(...) some_threads.push_back(std::thread(foo_func));
    for(...) some_threads.join();
}

The compiler is giving me the error:

编译器给了我错误：

'no matching call to std::thread::thread()'

'没有对 std::thread::thread() 的匹配调用'

Apparently there is 'no known conversion for argument 1 from <unresolved overloaded function type>to void (foo::*&&)'.

显然，参数 1 从<unresolved overloaded function type>到'没有已知的转换void (foo::*&&)'。

Erm, yeah, I have no idea what that means apart from the compiler is having trouble understanding how to resolve foo_func - I think.

嗯，是的，除了编译器无法理解如何解决 foo_func 之外，我不知道这意味着什么 - 我想。

How can I help the compiler understand what I am trying to do, so it won't bother me with any more errors. No doubt the code I have written is not legal, and if that is the case could someone explain why that is the case to me. Thanks!

我怎样才能帮助编译器理解我想要做的事情，这样它就不会再有任何错误了。毫无疑问，我编写的代码是不合法的，如果是这样的话，有人可以向我解释为什么会这样。谢谢！

回答by hmjd

foo_funcis a (non-static) member function, and it needs an instance of fooon which to operate. This instance must be provided to the thread constructor. If you refer to the std::thread::threadreference page it explains what code is executed in the new thread. The relevant point is that which refers to fbeing a pointer to member function:

foo_func是一个（非static）成员函数，它需要一个实例foo来操作。此实例必须提供给线程构造函数。如果您参考std::thread::thread参考页，它会解释在新线程中执行的代码。相关的一点是指的f是指向成员函数的指针：

• If fis pointer to a member function of class T, then it is called. The return value is ignored. Effectively, the following code is executed:
  • (t1.*f)(t2, ..., tN)if the type of t1is either T, reference to Tor reference to type derived from T.
  • ((*t1).*f)(t2, ..., tN)otherwise.

• 如果f是指向 class 成员函数的指针T，则调用它。返回值被忽略。有效地，执行以下代码：
  • (t1.*f)(t2, ..., tN)如果 的类型t1是T，则引用T或引用派生自 的类型T。
  • ((*t1).*f)(t2, ..., tN)除此以外。

so it is clear that the instance is required.

所以很明显实例是必需的。

Change to:

改成：

for(...) some_threads.push_back(std::thread(&foo::foo_func, this));

Simple example:

简单的例子：

#include <iostream>
#include <thread>
#include <vector>

class foo
{
public:
    void make_foo_func_threads()
    {
        for (int i = 0; i < 5; ++i)
            some_threads.push_back(std::thread(&foo::foo_func, this));
        for (auto& t: some_threads) t.join();
    }

private:
    void foo_func() { std::cout << "Hello\n"; }
    std::vector<std::thread> some_threads;
};

int main()
{
    foo f;
    f.make_foo_func_threads();
}