Thread: Casting temporary into base class reference

Hi,
On MSVC++, this compiles and runs as expected (even though we really know an acid is never a base):

Code:

#include <iostream>

using namespace std;

struct base
{
    virtual void doit() = 0;
};

struct acid : public base
{
    void doit() { cout << "I did it!" << endl; }
};

void stuff(base & b)
{
    b.doit();
}

int main()
{
    stuff(acid());
    return 0;
}

However, on GCC, I get the error:

Code:

error: invalid initialization of non-const reference of type ‘base&’ from a temporary of type ‘acid’|

Then, of course, making it work is just a matter of:

Code:

//. . . . . 
acid a;
stuff(a);
//. . . .

And that compiles fine. Why this disparity? Is there any way to make the top code compile in GCC?

GCC (and current C++ standard) doesn't accept temporaries for non-const references. Allowing this is VC++ extension.

What you need to do is make stuff take a const base& and make the doit method const, so you would be able to call it on a const object. Otherwise you simply can't use a temporary.

Thanks.

If you set compiler warnings to max (Properties -> C/C++ -> General), the compiler will warn about this.
If you disallow language extensions (Properties -> C/C++ -> Language), it won't compile.