Is there a standard formatting function or operator that will round up? (or down?)

Question

I am using ostringstream to output a number to 2 decimal places as follows

std::ostringstream ostr;

ostr << std::fixed << std::setprecision(2);
ostr << cylinderLength;

So, if cylinderLength = 0.594, the above outputs 0.59 as expected.

Is there an operator or function that will round up or down in the last desired decimal place?

In this case, the above example would print out 0.60 instead.

You need [ceil()](http://www.cplusplus.com/reference/cmath/ceil/) — Alok Save, Jan 12 '13 at 06:38
So you want to round up or down at a specific number of decimal places? — goji, Jan 12 '13 at 06:42
Yes, I thought of ceil, but that is defined as "returns the smallest integral value that is not less than x". I want the rounding to be applied in the last desired decimal place. — , Jan 12 '13 at 06:42
@Troy Yes, exactly. So 0.594 becomes 0.60 (using 2 decimal places) — , Jan 12 '13 at 06:45

score 6 · Accepted Answer · edited Jan 12 '13 at 06:41

6

Try:

// Round towards +infinity (to 1 decimal place (use 100 for 2 decimal places)
ceil(double * 10) / 10


// Round towards -infinity (to 1 decimal place (use 100 for 2 decimal places)
floor(double * 10) / 10

edited Jan 12 '13 at 06:41

Martin York

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answered Jan 12 '13 at 06:37

Yes, this clearly works - thank you. But there is no function or method that does this directly? I want to experiment with different precisions of rounding so this is a bit ungainly. – Jan 12 '13 at 06:47
@AndrewS. You can write a wrapper which does this. – Karthik T Jan 12 '13 at 06:50

Is there a standard formatting function or operator that will round up? (or down?)

1 Answers1