Compiler error or just unexpected result due to allowed optimization ???

[Bob Langelaan]

If I have the following code:

int var2 = 12;
int var3 = 20;

cout << '\n' << var2++ << " " << ++var2;
cout << '\n' << var2;

cout << "\n\n" << --var3 << " " << var3--;
cout << '\n' << var3;

I expect the output:

12 14
14

19 19
18

But with Microsoft Visual Studio 2013 I get instead:

13 14
14

18 20
18

I apologize if this question has been posted before.

Thanks,
Bob

[Paavo Helde]

Bob Langelaan <bobl...@gmail.com> wrote in news:e97438d7-404f-4a80-bc21-
cc697a...@googlegroups.com:

> If I have the following code:
>
> int var2 = 12;
> int var3 = 20;
>
> cout << '\n' << var2++ << " " << ++var2;
> cout << '\n' << var2;
>
> cout << "\n\n" << --var3 << " " << var3--;
> cout << '\n' << var3;

The behavior is undefined, anything can happen.

If instead of an int a class with user-defined ++ and -- operators was
used, then the behavior would be just unspecified and there would be a
couple of possible outputs, depending on which arguments happen to be
evaluated first.

IOW: don't write such code.