I'd like to create Foo
objects in C# from an unmanaged array of Foo
structs created in C++. This is how I think it should work:
On the C++ side:
extern "C" __declspec(dllexport) void* createFooDetector()
{
return new FooDetector();
}
extern "C" __declspec(dllexport) void releaseFooDetector(void* fooDetector)
{
FooDetector *fd = (FooDetector*)fooDetector;
delete fd;
}
extern "C" __declspec(dllexport) int detectFoo(void* fooDetector, Foo **detectedFoos)
{
FooDetector *fd = (FooDetector*)fooDetector;
vector<Foo> foos;
fd->detect(foos);
int numDetectedFoos = foos.size();
Foo *fooArr = new Foo[numDetectedFoos];
for (int i=0; i<numDetectedFoos; ++i)
{
fooArr[i] = foos[i];
}
detectedFoos = &fooArr;
return numDetectedFoos;
}
extern "C" __declspec(dllexport) void releaseFooObjects(Foo* fooObjects)
{
delete [] fooObjects;
}
On C# side: (I ommitted some fancy code making it possible to call the C++ functions from within C# for better readability);
List<Foo> detectFooObjects()
{
IntPtr fooDetector = createFooDetector();
IntPtr detectedFoos = IntPtr.Zero;
detectFoo(fooDetector, ref detectedFoos);
// How do I get Foo objects from my IntPtr pointing to an unmanaged array of Foo structs?
releaseFooObjects(detectedFoos);
releaseFooDetector(fooDetector);
}
But I don't know how to retrieve the objects from the IntPtr detectedFoos
. It should be possible somehow... Any hints?
UPDATE
Let's assume, Foo
is a simple detection rectangle.
C++:
struct Foo
{
int x;
int y;
int w;
int h;
};
C#:
[StructLayout(LayoutKind.Sequential)]
public struct Foo
{
public int x;
public int y;
public int width;
public int height;
}
Is it possible to read from unmanaged memory and create new managed objects from it before releasing the unmanaged memory?
I don't know how may Foo
objects will be detected, so I don't know, how much memory to allocate in C# before calling detectFoo()
. That's why I alloc/free memory in C++ and just pass a pointer to it. But somehow I can't retrieve the detectedFoo
s pointer address under C#. How do I do that?
You must re-declare Foo
in your C# project. Assuming you know the count of Foo
s and the value of sizeof(Foo)
you should be able to use System.Runtime.Interopservices.Marshal.PtrToStructure()
to retrieve your Foo
structures one at a time.
You have to define your struct again in C#, and it depends on your stuct. Your struct have to be blitable (the memory layout of the C# struct ave to be the same as it is for the C struct)
Have a look at "Marshalling structs"
Or post your real "Foo" struct and i can show you the C# version
UPDATE:
Because your struct seems to be blitable, you can simple cast the pointer to unmanaged memory to a pointer to the struct defined in c#:
If it is ok for your application to use unsafe code you can write:
unsafe List<Foo> detectFooObjects()
{
List<Foo> res = new List<Foo>()
IntPtr fooDetector = createFooDetector();
IntPtr detectedFoos = IntPtr.Zero;
int nNumFoos = detectFoo(fooDetector, ref detectedFoos );
for(int i=0;i<nNumFoos;i++)
{
Foo** ppDetectedFoos = detectedFoos.ToPointer();
Foo* pFoo = *ppDetectedFoos
res.Add(*pFoo); //copies the struct because is a struct
ppDetectedFoos++:
}
releaseFooObjects(detectedFoos);
releaseFooDetector(fooDetector);
return res;
}
我最终通过使用C ++ / CLI包装器类解决了我的问题。
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