Const reference to temporary

Question

After reading this article on Herb Sutter's blog, I experimented a bit and ran into something that puzzles me. I am using Visual C++ 2005, but I would be surprised if this was implementation dependent.

Here is my code:

#include <iostream>

using namespace std;

struct Base {
    //Base() {}
    ~Base() { cout << "~Base()" << endl; }
};

int main()
{
    const Base & f = Base();
}

When run, it displays "~Base()" twice... But if I un-comment the constructor, it displays it only once!

Does anyone have an explanation for this?

Answer 1

This IS implementation dependent.

The standard allows a copy to occur when binding a temporary to a const reference. In your case, VC++ performs a copy only when the constructor is implicitly defined. This is unexpected, but permitted.

C++1x will fix this.

Answer 2

Im using mingw 3.14 gcc 3.4.5 and my objects are not being copied with or without constructors. any idea why? Would this cause the program to be memory-unsafe?