‘const float’值不同于’float’当转换为’int’在C#

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你能解释为什么会发生这种情况吗? @H_404_2@static void Main() { const float xScaleStart = 0.5f; const float xScaleStop = 4.0f; const float xScaleInterval = 0.1f; const float xScaleAmplitude = xScaleStop - xScaleStart; const float xScaleSizeC = xScaleAmplitude / xScaleInterval; float xScaleSize = xScaleAmplitude / xScaleInterval; Console.WriteLine(">const float {0},(int){1}",xScaleSizeC,(int)xScaleSizeC); Console.WriteLine("> float {0},xScaleSize,(int)xScaleSize); Console.ReadLine(); }

输出

@H_404_2@>const float 35,(int)34 > float 35,(int)35

我知道0.1的二进制表示实际上是0.09999990463256835937,虽然为什么会发生使用’const float’而不是’float’?这是否被认为是编译器错误

对于记录,代码编译成:

@H_404_2@private static void Main(string[] args) { float xScaleSize = 35f; Console.WriteLine(">const float {0},35f,34); Console.WriteLine("> float {0},(int)xScaleSize); Console.ReadLine(); }

解决方法

“为什么”这基本上归结为这样的事实,即使用浮点数据时,可以使用具有比为float或double指定的精度更高的精度的内部表示。这在虚拟执行系统(VES)规范( Partition I第12节)中明确规定:

floating-point numbers are represented using an internal floating-point
type. In each such instance,the nominal type of the variable or expression is either float32 or float64,but its
value can be represented internally with additional range and/or precision

然后,我们有:

The use of an internal representation that is wider than float32 or float64 can cause differences in
computational results when a developer makes seemingly unrelated modifications to their code,the result of
which can be that a value is spilled from the internal representation (e.g.,in a register) to a location on the
stack.

现在,根据C# language specification

The compile-time evaluation of constant expressions uses the same rules as run-time evaluation of non-constant expressions,except that where run-time evaluation would have thrown an exception,compile-time evaluation causes a compile-time error to occur.

但是如上所述,规则实际上允许更多的精度被有时使用,并且当使用这种增强的精度时,实际上不是在我们的直接控制下。

显然,在不同的情况下,结果可能恰恰与您观察到的结果相反 – 编译器可能已经降低了精度,而运行时可以保持更高的精度。

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