Question

On VC++ 2008, ceil(-0.5) is returning -0.0. Is this usual/expected behavior? What is the best practice to avoid printing a -0.0 to i/o streams.

Answer 1

ceil in C++ comes from the C standard library.

The C standard says that if a platform implements IEEE-754 arithmetic, ceil( ) behaves as though its argument were rounded to integral according to the IEEE-754 roundTowardPositive rounding attribute. The IEEE-754 standard says (clause 6.3):

the sign of the result of conversions,
the quantize operation, the
roundToIntegral operations, and the
roundToIntegralExact is the sign of
the first or only operand.

So the sign of the result should always match the sign of the input. For inputs in the range (-1,0), this means that the result should be -0.0.