Why does Release/Debug have a different result for std::min?

Question

Here is the test program:

void testFunc()
{
    double maxValue = DBL_MAX;
    double slope = std::numeric_limits::quiet_NaN();

    std::cout          


        

Answer 1

You didn't specify which floating point representation format your processor uses. But, since you use Visual Studio, I'll assume that you use Windows, and then I'll assume that your processor uses IEEE 754 representation.

In IEEE 754, NaN is unordered in respect to every number. This means that (NaN < f) == false and (f < NaN) == false for any value of f. Pedantically, this means that floating point numbers that support NaN do not meet the requirements of LessThanComparable which is a requirement for std::min. Practically std::min behaves as specified in the standard as long as neither argument is NaN.

Since one of the arguments is NaN in your code, the result is unspecified by the standard - it could be one or the other depending on any external factors such as release vs debug build, version of compiler, phase of the moon, etc.