我想是能够转换一个高价值的无符号整数有符号整数（即使用最高位的值）。 在这种情况下，我不关心该值大于符号整数型的最大值。 我只是希望它转换到任何位值代表作为签署整数。 换句话说，我希望它导致一个负数。
然而，VB.NET，该CType操作不工作的方式（或任何类似的其他转换功能CShort和CInteger ）。 当您尝试转换一个无符号的值比期望的签署型的最高值时，它抛出一个OverflowException ，而不是返回一个负数。 例如：
Dim x As UShort = UShort.MaxValue
Dim y As Short = CShort(x) ' Throws OverflowException
值得一提的，那就是，在DirectCast操作不能用于铸造符号和无符号类型之间的值，因为无论是类型继承或实现其他。 例如：
Dim x As UShort = UShort.MaxValue
Dim y As Short = DirectCast(x, Short) ' Won't compile: "Value of type 'UShort' cannot be converted to 'Short'
我已经想通了，做我想做什么的一种方式，但似乎不必要的丑陋。 下面是我如何开始工作：
Dim x As UShort = UShort.MaxValue
Dim y As Short = BitConverter.ToInt16(BitConverter.GetBytes(x), 0) ' y gets set to -1
就像我说的，这样的作品，但如果有在VB.NET做的更简单，更清洁的方式，我很想知道它是什么。
Answer 1:
经常使用的BitConverter是怎么回事，如果你使用的是有很多是有点不方便-特别是对性能。 如果是我，我会非常想添加一个实用程序在C＃中，可以做直接转换库（通过unchecked ，虽然unchecked通常是在C＃中默认反正 ），并参考该库这一点。 另一种选择可能是滥用“联盟”结构; 下面应该翻译成VB相当容易：
[StructLayout(LayoutKind.Explicit)]
struct EvilUnion
{
[FieldOffset(0)] public int Int32;
[FieldOffset(0)] public uint UInt32;
}
...
var evil = new EvilUnion();
evil.Int32 = -123;
var converted = evil.UInt32;
即
<System.Runtime.InteropServices.StructLayout(Runtime.InteropServices.LayoutKind.Explicit)>
Structure EvilUnion
<System.Runtime.InteropServices.FieldOffset(0)>
Public Int32 As Integer
<System.Runtime.InteropServices.FieldOffset(0)>
Public UInt32 As UInteger
End Structure
...
Dim evil As New EvilUnion
evil.Int32 = -123
Dim converted = evil.UInt32
Answer 2:
早在VB6的日子里，我们不得不这样写程序的所有时间：
Private Function ToShort(ByVal us As UShort) As Short
If (us And &H8000) = 0 Then
Return CType(us, Short)
Else
Return CType(CType(us, Integer) - UShort.MaxValue - 1, Short)
End If
End Function
至少在.NET中，您可以创建一个扩展方法出这使它更好过
Answer 3:
非常简单：
对于32位
Dim uVal32 As UInt32 = 3000000000
Dim Val32 As Int32 = Convert.ToInt32(uVal32.ToString("X8"), 16)
val32结束= -1294967296
对于16位
Dim uVal16 As UInt16 = 60000
Dim Val16 As Int16 = Convert.ToInt16(uVal16.ToString("X4"), 16)
val16结束= -5536
Answer 4:
我发现这一点： ??在VB.NET类型转换的问题？
关于网页下半部是这样的：
老，VB“适当”出十六进制“侧步”的把戏，然后再返回仍然有效！
Dim unsigned as UInt16 = 40000
Dim signed as Int16 = CShort(Val("&H" & Hex(unsigned)))
看来工作非常漂亮！
Answer 5:
我认为，最简单的方法如下：
Public Function PutSign(ByVal number As UShort) As Short
If number > 32768 Then 'negative number
Return (65536 - number) * -1
Else
Return number
End If
End Function
Answer 6:
我只是碰到这样的问题，也是和现在看来似乎不是很优化，并没有像BitConverter方法。 所以，我认为，在内存中的数据的存储是真的既为int和uint仅有4个字节。
下面似乎是最有效的方式来处理这一点，并在可使用Marshal类所有.NET语言的作品...
Dim x as UInteger = &H87654321
Dim gch as GCHandle = GCHandle.Alloc(x, Pinned)
Dim y as Integer = Marshal.ReadInt32(gch.AddrOfPinnedObject)
gch.Free
希望这可以帮助别人。
Answer 7:
通常情况下，这将与在高级语言流来完成，但是Net框架暴露的方式，而不使用元帅中间流对象这样做。
Imports System.Runtime.InteropServices
Module Module1
Sub Main()
Dim given As Int16 = -20
Dim buffer As IntPtr = Marshal.AllocCoTaskMem(Marshal.SizeOf(given))
Marshal.StructureToPtr(given, buffer, False)
Dim result As UInt16 = Marshal.PtrToStructure(buffer, GetType(UInt16))
MsgBox(result)
End Sub
End Module
令我惊讶的是，使用元帅似乎比使用运算更高效的基础上，我得到了统计数据
4 seconds of v1 yielded: 2358173 conversions
4 seconds of v2 yielded: 4069878 conversions
从测试：
Imports System.Runtime.InteropServices
Module Module1
Function v1(given As Int16) As UInt16
Dim buffer As IntPtr = Marshal.AllocCoTaskMem(Marshal.SizeOf(given))
Marshal.StructureToPtr(given, buffer, False)
Dim result As UInt16 = Marshal.PtrToStructure(buffer, GetType(UInt16))
v1 = result
End Function
Function v2(given As Int16) As UInt16
If given < 0 Then
given = (Not given) + 1
End If
v2 = given
End Function
Sub Main()
Dim total0 As Integer
Dim total1 As Integer
Dim t0 As DateTime = DateTime.Now()
While ((DateTime.Now() - t0).TotalSeconds() < 4)
v1(-Rnd() * Int16.MaxValue)
total0 = total0 + 1
End While
Console.WriteLine("4 seconds of v1 yielded: " & total0 & " conversions")
t0 = DateTime.Now()
While ((DateTime.Now() - t0).TotalSeconds() < 4)
v2(-Rnd() * Int16.MaxValue)
total1 = total1 + 1
End While
Console.WriteLine("4 seconds of v2 yielded: " & total1 & " conversions")
Console.ReadKey()
End Sub
End Module
更奇怪的是，少帅做法似乎可以忽略不计的C＃样式转换为有效的。 在我第一次运行时，元帅的做法是比较慢，但在第二轮，元帅的做法是快。 这是第二次运行的结果
4 seconds of v1 yielded: 1503403 conversions
4 seconds of v2 yielded: 1240585 conversions
4 seconds of v3 yielded: 1592731 conversions
使用此代码
using System;
using System.Runtime.InteropServices;
class Program
{
static DateTime startTime = DateTime.Now;
static double time {
get {
return (DateTime.Now - startTime).TotalMilliseconds;
}
}
static ushort v1(short given) {
if (given > 0) {
return (ushort)given;
}
return (ushort)(~given + 1);
}
static ushort v2(short given) {
var buffer = Marshal.AllocCoTaskMem(Marshal.SizeOf(given));
Marshal.StructureToPtr(given, buffer, false);
ushort result = (ushort)Marshal.PtrToStructure(buffer, typeof(ushort));
return result;
}
static ushort v3(short given)
{
return (ushort)given;
}
static void Main(string[] args)
{
int total0 = 0;
int total1 = 0;
int total2 = 0;
double t0;
t0 = time;
while (time - t0 < 4000) {
v1((short)(-new Random().NextDouble() * Int16.MaxValue));
++total0;
}
Console.WriteLine("4 seconds of v1 yielded: " + total0 + " conversions");
t0 = time;
while (time - t0 < 4000) {
v2((short)(-new Random().NextDouble() * Int16.MaxValue));
++total1;
}
Console.WriteLine("4 seconds of v2 yielded: " + total1 + " conversions");
t0 = time;
while (time - t0 < 4000) {
v3((short)(-new Random().NextDouble() * Int16.MaxValue));
++total2;
}
Console.WriteLine("4 seconds of v3 yielded: " + total2 + " conversions");
Console.ReadKey();
}
}
我们带来的王。
// ConsoleApplication3.cpp : main project file.
#include "stdafx.h"
using namespace System;
using namespace System::Runtime::InteropServices;
unsigned __int16 v4(__int16 given) {
return (unsigned __int16)given;
}
public ref class Program
{
public:
static DateTime startTime = DateTime::Now;
static property double time {
double get() {
return (DateTime::Now - startTime).TotalMilliseconds;
}
}
static UInt16 v1(Int16 given) {
if (given > 0) {
return given;
}
return (UInt16)(~given + 1);
}
static UInt16 v2(Int16 given) {
IntPtr buffer = Marshal::AllocCoTaskMem(Marshal::SizeOf(given));
Marshal::StructureToPtr(given, buffer, false);
Type ^t = UInt16::typeid;
UInt16 result = (UInt16)Marshal::PtrToStructure(buffer, t);
return result;
}
static UInt16 v3(Int16 given)
{
return (UInt16)given;
}
typedef String ^string;
static void _Main(array<string> ^args)
{
int total0 = 0;
int total1 = 0;
int total2 = 0;
int total3 = 0;
double t0;
t0 = time;
while (time - t0 < 4000) {
Double d = (gcnew Random())->NextDouble();
v1((short)(-d * Int16::MaxValue));
++total0;
}
Console::WriteLine("4 seconds of v1 yielded: " + total0 + " conversions");
t0 = time;
while (time - t0 < 4000) {
v2((short)(-((gcnew Random())->NextDouble()) * Int16::MaxValue));
++total1;
}
Console::WriteLine("4 seconds of v2 yielded: " + total1 + " conversions");
t0 = time;
while (time - t0 < 4000) {
v3((short)(-((gcnew Random())->NextDouble()) * Int16::MaxValue));
++total2;
}
Console::WriteLine("4 seconds of v3 yielded: " + total2 + " conversions");
t0 = time;
while (time - t0 < 4000) {
v4((short)(-((gcnew Random())->NextDouble()) * Int16::MaxValue));
++total3;
}
Console::WriteLine("4 seconds of v4 yielded: " + total3 + " conversions");
Console::ReadKey();
}
};
int main(array<System::String ^> ^args)
{
Program::_Main(args);
return 0;
}
好了，结果是非常有趣
4 seconds of v1 yielded: 1417901 conversions
4 seconds of v2 yielded: 967417 conversions
4 seconds of v3 yielded: 1624141 conversions
4 seconds of v4 yielded: 1627827 conversions
Answer 8:
Necromancing。
作为补充，马克Gravell的答案，如果你想知道如何做到这一点的头部：
你可以把它写一般为：
<unsigned_type> value = unchecked(<unsigned_type>.MaxValue + your_minus_value + 1);
由于类型检查的，代码是这样的：
public uint int2uint(int a)
{
int sign = Math.Sign(a);
uint val = (uint) Math.Abs(a);
uint unsignedValue;
if(sign > 0) // +a
unsignedValue = unchecked(UInt32.MaxValue + val + 1);
else // -a, a=0
unsignedValue = unchecked(UInt32.MaxValue - val + 1);
return unsignedValue;
}
然后，如果你想这样做的头，你可以做这样的：
BigInt mentalResult= <unsigned_type>.MaxValue + your_value;
mentalResult = mentalResult % <unsigned_type>.MaxValue;
if (your_value < 0) // your_value is a minus value
mentalResult++;
// mentalResult is now the value you search
Answer 9:
在下面这个例子中，由Marc Gravell答案被扩展以证明在VB用处：
<System.Runtime.InteropServices.StructLayout(Runtime.InteropServices.LayoutKind.Explicit)>
Structure vbUnion16
<System.Runtime.InteropServices.FieldOffset(0)>
Public UnSigned16 As UInt16
<System.Runtime.InteropServices.FieldOffset(0)>
Public Signed16 As Int16
<System.Runtime.InteropServices.FieldOffset(0)>
Public High8 As Byte
<System.Runtime.InteropServices.FieldOffset(1)>
Public Low8 As Byte
End Structure
从概念上讲，它是由“转换”类型的可变的不同。 更确切地说，该方法显示出存储的实体。 在访问它各部分的同时，不同的方式提供。
由于该操作是“访问”不“转化”，这是非常快的，精干高效的（见成员对马克的发表评论）。
字节序是由编译器处理。
Answer 10:
如果你需要经常这样做，你可以创建高性能的扩展方法类似这样：
Imports System.Runtime.CompilerServices
Module SignConversionExtensions
<StructLayout(LayoutKind.Explicit)> _
Private Structure Union
<FieldOffset(0)> Public Int16 As Int16
<FieldOffset(0)> Public UInt16 As UInt16
End Structure
<Extension()> Public Function ToSigned(ByVal n As UInt16) As Int16
Return New Union() With {.UInt16 = n}.Int16
End Function
<Extension()> Public Function ToUnsigned(ByVal n As Int16) As UInt16
Return New Union() With {.Int16 = n}.UInt16
End Function
End Module
这使得签约，无符号的转换非常简单：
Dim x As UShort = UShort.MaxValue ' unsigned x = 0xFFFF (65535)
Dim y As Short = x.ToSigned ' signed y = 0xFFFF (-1)
Answer 11:
不知道VB，但我希望它是类似于C＃，因为它是.NET代码。 在C＃中，你可以简单地使用类型转换：
UInt16 ui = 65000;
Int16 i = (Int16)ui;
完成。
文章来源: How to convert unsigned integer to signed integer without OverflowException
