C++ RoundUp 就像在 Excel 那个楼层的负数和正数上的 ceil

Question

Excel has a function called ROUNDUP, which not being a mathematician I would call a true round up or at least more logical to me, in that it makes makes a positive value like 0.5 value into 1 and a negative value like -0.5 into -1. So in other words the Excel ROUNDUP do a C++ ceil equivalent on the 0.5 value, and C++ floor equivalent on the -0.5 value.

Is there nothing built into C++ like that? Yes I know I can make my own function, but that defeats the reason I need this as a custom function that determines if number to be rounded is a positive or a negative, then needs an IF statement!

Answer 1

There's not built in function to round away from zero. But you can write your own without any obvious if statements.

double RoundAwayFromZero(double v) {
    auto s = std::copysign(1.0, v);
    return s * std::ceil(v * s);
}

This uses copysign to get a properly signed 1.0 value that is then used to make the value positive, round it away from 0 using ceil , then restore the proper sign to the result.