CODEWITHSUNDEEP
c++c++11
이동근
이동근

Reputation: 113

How detect my std::function is still available?

Im using std::function and std::bind for my async thread callback system. but sometimes my system delete my object even some threads are not done. here some example code

#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
}

please help me to do this.

Upvotes: 2

Views: 241

Answers (2)

Jarod42
Jarod42

Reputation: 218268

Instead of an raw pointer, you may use std::weak_ptr, something like:

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 :)
}

Upvotes: 6

Oguz Ozcan
Oguz Ozcan

Reputation: 1547

This is because you are deleting pChar* pointer which is used in your callback() method. Delete pChar after you are done with everything.

Upvotes: -1

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