Question

I was reading “Bjarne Stroustrup’s C++ Style and Technique” FAQ where he mentioned about this FAQ
What’s the value of i++ + i++?

In this he has mentioned “…the order of evaluation of function arguments are undefined.” when he is refering to f(v[i],i++); example.

I am aware of that the order of evaluation of function arguments is unspecified not undefined but in this case is it undefined because we are relying on value of i so as to which v[i] to pass or its an error in the FAQ itself?

Answer 1

The order of evaluation of function arguments is unspecified but the behaviour of the expression is undefined. Bjarne has just got it wrong. 🙂

Check out this thread to understand the difference between Unspecified Behaviour and Undefined Behaviour.

I once asked Bjarne the difference between unspecified and undefined and this was his reply..

Personally, I don’t bother with the distinction between "undefined" and "unspecified"; do you know what it is? That code should be taken out and shot in either case: (carefully avoiding the words "undefined" and "unspecified")

…..

You don’t need to know: just avoid both. If someone really want to know they can look up the definitions in the C++ or C standards (my bet would be that the C and C++ standards will disagree on unimportant details).