Question about the object adress of a return object with the type of boost::function &

Question

Why the addresses of this two variable(i.e hoofunc and Ctx::hookFunc4Boost) are not same whereas the Ctx::getBoostHookFun() return a left reference to Ctx::hookFunc4Boost?

I intend to avoid the copy of a temporary object by returning a left reference to Ctx::hookFunc4Boost.

Here is the code snippet:

#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <iostream>

class Ctx
{
public:
const boost::function<void((void*))>& getBoostHookFun(void)
{
    std::cout << "inner hookFunc4Boost:" << (void*)(&hookFunc4Boost) << std::endl;
    return hookFunc4Boost;
}

private:
boost::function<void(void*)> hookFunc4Boost;

};

int main()
{
    Ctx ctx;
    Ctx *pCtx = &ctx;
    const boost::function<void((void*))> hookFunc = pCtx->getBoostHookFun();
    std::cout << "outer hookFunc:" << (void*)(&hookFunc) << std::endl;
}

Here are the outputs:

inner hookFunc4Boost:0x7fffffffdf28
outer hookFunc:0x7fffffffd540

Answer 1

With the help of JaMiT, I think I find the answer.

Here is a demo code(https://coliru.stacked-crooked.com/view?id=12bc35c31c9eb605):

#include <iostream>

class Ctx
{
public:
Ctx(int cnt):m_cnt(cnt){}

const int& getCnt(void)
{
    std::cout << "inner:" << (void*)&m_cnt << std::endl;
    return m_cnt;
}

private:
int m_cnt;

};

int main()
{
    Ctx ctx(6);
    Ctx *pCtx = &ctx;
    const int cnt = pCtx->getCnt();
    std::cout << "outer:" << (void*)&cnt << std::endl;
}

The variable cnt and Ctx::m_cnt are two different variables. So their addresses should be different. It still needs to call copy constructor when invoking const int cnt = pCtx->getCnt();. Am I right?

Answer 2

To avoid a copy just change your variable to a reference:

const auto& hookFunc = pCtx->getBoostHookFun();