Boost :: format gives different results than round

Question

I would like to understand why

double nbr = 102262.5;

boost::format("%.0f") % nbr;

gives 102262, but round(102262.5)gives102263.0

If we take another approximate value 34087.5

boost::format("%.0f") % nbr

gives 34088and round(34087.5)gives the same34088

Does this mean that round implements a more complex algorithm to ensure that there is no format or printf in the near future?

Answer 1

There is a thing called “half to even” or “round half to odd” ( link ).

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Answer 2

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