Positive integers that multiply to a negative value

Question

I am learning C++ by reading Stroustrup\'s \"Principles and Practice Using C++\".

In the section about pre- and post-conditions there is the following example of functio

Answer 1

Since C++11 there is a boolean value you can test:

std::numeric_limits::is_modulo

If this value is true then signed arithmetic behaves in a wraparound fashion, and there is no undefined behaviour in the original code. A negative value could indeed be produced and so the test in the original code is meaningful.

For further discussion of is_modulo see here