C++: how can I test if a number is power of ten?

Question

I want to test if a number double x is an integer power of 10. I could perhaps use cmath\'s log10 and then test if x == (int) x?

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Answer 1

Your solution sounds good but I would replace the exact comparison with a tolerance one.

double exponent = log10(value);
double rounded = floor(exponent + 0.5);
if (fabs(exponent - rounded) < some_tolerance) {
    //Power of ten
}