C++ storing a const& to a temporary

Question

Recently I have run into a problem in a project. The code there is much more complicated than the following example but I hope the problem (if there is one) is the same.

#include <iostream>
class mObject
{
public:
    mObject(){ std::cout << "mObject ctor\n"; }
    mObject(const mObject& other){ std::cout << "mObject copy ctor\n"; }
    ~mObject(){ std::cout << "mObject dtor\n"; }
};

struct cFoo{
    cFoo(const mObject& obj):obj_(obj){}
    const mObject& get() { return obj_;}
    const mObject& obj_;
};

mObject giveme() { return mObject(); }
void func2(const mObject& p) { mObject g = p; }

int main()
{
    cFoo k(giveme());
    func2(k.get());
    return 0;
}

This gives me the following code:

mObject ctor
mObject dtor
mObject copy ctor
mObject dtor

So the original "temporary" mObject instance dies before func2 usese it. I thought life time of a temporary object is extended if there is a const& to it. Assigning return of giveme() to a local const& in funtion main solves this problem. Then the temporary lives until the end of the main's scope. So what is going on here???

Answer 1

Within the same scope of the same function, you can extend the lifetime of an anonymous temporary by binding it to a const reference; for the avoidance of doubt this behaviour is not transitive across function calls.