[英]vb.net byte[] to C++ char*
I am calling an unmanaged C++ dll that expects a char* as one of its parameters and I want to push a byte[] into it. 我正在调用一个非托管的C ++ dll,它将char *作为其参数之一,我想将byte []推入其中。 The project is written in VB.NET.
该项目是用VB.NET编写的。
What type of marshalling will work for this? 哪种编组将对此起作用?
If you need to pin a managed structure in order to pass it as a parameter you can use the following code. 如果需要固定托管结构以将其作为参数传递,则可以使用以下代码。
// (c) 2007 Marc Clifton
/// <summary>
/// A helper class for pinning a managed structure so that it is suitable for
/// unmanaged calls. A pinned object will not be collected and will not be moved
/// by the GC until explicitly freed.
/// </summary>
internal class PinnedObject<T> : IDisposable where T : struct
{
protected T managedObject;
protected GCHandle handle;
protected IntPtr ptr;
protected bool disposed;
public T ManangedObject
{
get
{
return (T)handle.Target;
}
set
{
Marshal.StructureToPtr(value, ptr, false);
}
}
public IntPtr Pointer
{
get { return ptr; }
}
public int Size
{
get { return Marshal.SizeOf(managedObject); }
}
public PinnedObject()
{
managedObject = new T();
handle = GCHandle.Alloc(managedObject, GCHandleType.Pinned);
ptr = handle.AddrOfPinnedObject();
}
~PinnedObject()
{
Dispose();
}
public void Dispose()
{
if (!disposed)
{
if (handle.IsAllocated)
handle.Free();
ptr = IntPtr.Zero;
disposed = true;
}
}
}
}
You can then call the unmanaged code using PinnedObject.Pointer. 然后,您可以使用PinnedObject.Pointer调用非托管代码。 In your extern declaration, use IntPtr as the Type for that parameter.
在您的外部声明中,将IntPtr用作该参数的类型。
PinnedObject<BatteryQueryInformation> pinBatteryQueryInfo = new PinnedObject<BatteryQueryInformation>();
pinBatteryQueryInfo.ManangedObject = _structBatteryQueryInfo;
Unmanaged.Method(pinBatteryQueryInfo.Pointer);
In your PInvoke definition just declare the char* parameter as a byte[] and the standard marshaller will handle work. 在您的PInvoke定义中,只需将char *参数声明为byte [],标准编组将处理工作。
But this may or may not be the best idea. 但这可能不是最好的主意。 Is the C++ function expecting a string or is it expecting a buffer of data (C/C++ code often uses char* for a buffer, relying on the fact that a char is one byte)?
C ++函数是期望字符串还是期望数据缓冲区(C / C ++代码通常使用char *作为缓冲区,这取决于char是一个字节的事实)?
If it is a buffer then a byte[] is certainly correct, but if it expects a string then it may be clearer if you declare the parameter as a string (to be explicit) and use Encoding.ASCII.GetString() to convert the byte[] to a string. 如果它是一个缓冲区,那么byte []当然是正确的,但是如果它期望一个字符串,那么如果将参数声明为字符串(是明确的)并使用Encoding.ASCII.GetString()来转换参数,则可能会更清楚。 byte []转换为字符串。
Also if it C++ function expects a string and you decide to declare the parameter as a byte[], be sure the byte array ends with a zero, since that is how C/C++ determines the end of the string. 同样,如果C ++函数需要一个字符串,并且您决定将参数声明为byte [],请确保字节数组以零结尾,因为这是C / C ++确定字符串结尾的方式。
I'm not a .net expert, but I've needed to do something similar recently. 我不是.net专家,但是最近我需要做类似的事情。
It is not just a matter of serialization, you also have to stop the garbage collector from cleaning up your byte array while it is being used in C++ land... 这不仅仅是序列化的问题,当在C ++领域使用字节数组时,还必须停止垃圾回收器清理字节数组。
The below snippet of C# should help. 下面的C#代码片段应该会有所帮助。
// pin the byte[] (byteArray) GCHandle handle = GCHandle.Alloc(byteArray, GCHandleType.Pinned); IntPtr address = handle.AddrOfPinnedObject(); // Do your C++ stuff, using the address pointer. // Cleanup handle.Free();
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