为什么单个定义超出范围？

Question

The range of single data type is -3.4028235E+38 through -1.401298E-45 for negative values. Why does this code not result in a compile time error?

'(Option Strict On)

Dim s As Single
s = -5.4028235E+38

Answer 1

Because it is converted from a Double to a Single, which results in Single.NegativeInfinity . If you would explicitly define the datatype like this (or with a ! , details here ):

s = -5.4028235E+38F

It would result in an overflow and wouldn't compile.

From the MSDN page about conversions of the single data type:

Double Narrowing: out-of-range values are converted to Double.NegativeInfinity or Double.PositiveInfinity.

In addition, the Double values Double.NaN, Double.PositiveInfinity, and Double.NegativeInfinity covert to Single.NaN, Single.PositiveInfinity, and Single.NegativeInfinity, respectively.