Round double to 3 points decimal [duplicate]

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A common trick is to do it with maths:

value = round( value * 1000.0 ) / 1000.0;

Where round will handle negative and positive values correctly… Something like this (untested):

inline double round( double val )
{
    if( val < 0 ) return ceil(val - 0.5);
    return floor(val + 0.5);
}

You’ll still want to set the decimal places to 3 during output, due to floating point precision problems.

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