C++析构函数过早调用

Question

我已将代码简化为仍然存在问题的最小样本。此代码应打印“42”，但打印的是一个不同的数字。我还在析构函数中打印“Secret”对象的地址，以及何时访问它，以表明它被过早销毁。我在这里做错了什么，还是编译器有问题？

代码:

#include <iostream>    

using namespace std;    

struct Secret{
    int value;
    Secret(int value):value(value){}
    ~Secret(){
        cout<<"destructor:"<<(void*)this<<endl;
        value=0;
    }
};    

template<class Func>
class Copier{
public:
    Func func;
    Copier(Func func):func(func){}
    void run(){
        func();
    }
    auto copy(){
        auto output = [this](){
            func();
        };
        Copier<decltype(output)> out(output);
        return out;
    }    

};
auto makeSecretPrinter(){
    Secret secret(42);
    auto secretPrinter = [secret](){
        cout<<"reading object at address:"<<(void*)&secret<<endl;
        cout<<"the secret is:"<<secret.value<<endl;
    };
    return Copier<decltype(secretPrinter)>(secretPrinter).copy();
}    

int main(){
    makeSecretPrinter().run();
    return 0;
}

clang(版本 3.5-1ubuntu1)输出:

destructor:0x7fff9e3f9940
destructor:0x7fff9e3f9938
destructor:0x7fff9e3f9948
destructor:0x7fff9e3f9950
reading object at address:0x7fff9e3f9940
the secret is:0

GCC (Ubuntu 4.9.2-0ubuntu1~14.04) 4.9.2 输出:

destructor:0x7fff374facc0
destructor:0x7fff374facb0
destructor:0x7fff374faca0
destructor:0x7fff374fac90
reading object at address:0x7fff374facc0
the secret is:-1711045632

Answer 1

捕获 this 使用指针语义进行捕获。改变这个:

auto output = [this](){
    func();
};

这解决了问题:

auto output = [self=*this](){
    self.func();
};