我有一个名为rawbits的IntPtr,它指向10MB的数据数组,16位值.我需要从中返回一个托管的ushort数组.以下代码有效,但我想摆脱一个额外的BlockCopy. Marshal.Copy不支持ushort.我能做什么？ (仅供参考：rawbits由视频framegrabber卡填充到非托管内存中)
public const int width = 2056;
public const int height = 2048;
public const int depth = 2;
public System.IntPtr rawbits;
public ushort[] bits()
{
ushort[] output = new ushort[width * height];
short[] temp = new short[width * height];
Marshal.Copy(rawbits,temp,width * height);
System.Buffer.BlockCopy(temp,output,width * height * depth);
return output;
}
以下问题中给出的建议没有帮助. (编译错误).
C# Marshal.Copy Intptr to 16 bit managed unsigned integer array
[顺便说一句,短阵列中确实有无符号的16位数据. Marshal.Copy()不尊重标志,这就是我想要的.但我宁愿不只是假装短[]是一个ushort []]
解决方法
选项1 – 调用CopyMemory：
[DllImport("kernel32.dll",SetLastError = false)]
static extern void CopyMemory(IntPtr destination,IntPtr source,UIntPtr length);
public static void Copy<T>(IntPtr source,T[] destination,int startIndex,int length)
where T : struct
{
var gch = GCHandle.Alloc(destination,GCHandleType.Pinned);
try
{
var targetPtr = Marshal.UnsafeAddrOfPinnedArrayElement(destination,startIndex);
var bytesToCopy = Marshal.SizeOf(typeof(T)) * length;
CopyMemory(targetPtr,source,(UIntPtr)bytesToCopy);
}
finally
{
gch.Free();
}
}
不便携,但性能不错.
选项2 – 不安全和指针：
public static void Copy(IntPtr source,ushort[] destination,int length)
{
unsafe
{
var sourcePtr = (ushort*)source;
for(int i = startIndex; i < startIndex + length; ++i)
{
destination[i] = *sourcePtr++;
}
}
}
需要在项目构建属性中启用不安全选项.
选项3 – 反思(只是为了好玩,不要在生产中使用)：
Marshal类在内部对所有Copy(IntPtr,< array>,int,int)重载使用CopyToManaged(IntPtr,object,int)方法(至少在.NET 4.5中).使用反射我们可以直接调用该方法：
private static readonly Action<IntPtr,int> _copyToManaged =
GetCopyToManagedMethod();
private static Action<IntPtr,int> GetCopyToManagedMethod()
{
var method = typeof(Marshal).GetMethod("CopyToManaged",System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.NonPublic);
return (Action<IntPtr,int>)method.CreateDelegate(
typeof(Action<IntPtr,int>),null);
}
public static void Copy<T>(IntPtr source,int length)
where T : struct
{
_copyToManaged(source,destination,startIndex,length);
}
由于Marshal类的内部结构可以更改,因此该方法不可靠且不应使用,尽管此实现可能最接近其他Marshal.Copy()方法重载.
