c++ - 如何检测我的 std::function 是否仍然可用？

Question

我将 std::function 和 std::bind 用于我的异步线程回调系统。但有时我的系统会删除我的对象，即使有些线程没有完成。这里有一些示例代码

#include <iostream>
#include <functional>

using namespace std;

class Character {
public:
    Character() { a = 10; }

    void Print() { cout << a << endl; }

private:
    int a;

};

void main() {
    Character* pChar = new Character();

    std::function<void()> callback = std::bind(&Character::Print, pChar);
    callback(); // it's fine

    delete pChar;


    callback(); // fail


    if (callback)   // this if doesn't work
        callback();

    // i want to check callback is still available
}

请帮我做这件事。

Answer 1

您可以使用 std::weak_ptr 代替原始指针，例如:

void safePrint(std::weak_ptr<Character> w)
{
    auto pChar = w.lock();
    if (pChar) {
        pChar->Print();
    }
}

int main() {
    auto pChar = make_shared<Character>();

    auto callback = std::bind(&safePrint, std::weak_ptr<Character>(pChar));
    callback(); // it's fine

    pChar.reset(); 

    callback(); // won't print, and don't crash :)
}