C ++ ceil和负零

问题描述

在VC ++ 2008中， ceil（-0.5）正在返回 -0.0 。这是通常/预期的行为吗？避免将 -0.0 打印到i / o流中的最佳做法是什么。

解决方案

ceil 来自C标准库。

C标准说如果平台实现IEEE-754算术， ceil（）表现为根据IEEE-754 roundTowardPositive 舍入属性将其参数四舍五入为整数。 IEEE-754标准说明（第6.3节）：

因此，结果的符号应始终与输入的符号相匹配。对于范围（ - 1,0）中的输入，这意味着结果应为 -0.0 。

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.

解决方案

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):

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.

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